You know those United Way posters with a thermometer showing progress toward a fundraising goal? The image above is my attempt at a similarly easy-to-understand progress meter for the Iowa Nutrient Reduction Strategy (INRS). Based on changes to farming practices in the decade since the Iowa Nutrient Reduction Strategy was released, we should have met our goal for phosphorus but have only reduced nitrogen losses by 2%, not enough to undo the increases of the previous decade. These are best-case scenarios which do not account for manure, legacy sediment and nutrients, and interactions between practices.
Iowa State University is responsible for tracking the progress of the INRS, and has created a set of data dashboards covering dollars spent, minds changed, conservation practices on the land, and water quality trends in the rivers. These were updated in May of 2024. There is no top-line summary of where we stand relative to our goals, but wasn’t hard to make one. I just added up the numbers in a pair of tables labelled “change in modeled nitrogen/phosphorus load for practices since the baseline period.”
Baselines, Goals and Timelines
The timeline requires some explanation. The INRS was released in 2013, but the baseline period is 1980-1996. That’s because the Hypoxia Action Task Force was formed in 1997. The task force set a goal of reducing the size of the dead zone in Gulf to 5000 square kilometers (1,930 square miles). The target date for meeting that goal has been pushed back several times. Despite several dry years, the five-year average extent of the dead zone is still twice as big as the target. Last year it measured 6,705 square miles, larger than Connecticut or Hawaii.
To meet the goals for shrinking the dead zone, each state would need to reduce the amount of nitrogen and phosphorus lost down the Mississippi River by 45%. The Iowa Department of Natural Resources determined that mandatory upgrades for 102 municipal wastewater treatment systems and 28 industrial facilities could reduce state’s overall nitrogen load by 4% and phosphorus load by 16%. The remaining 41% reduction in nitrogen load and 29% reduction in phosphorus load would need to come from controlling non-point sources of pollution like agricultural runoff.
Iowa State University was tasked with answering the question: “based on what we know about the performance of various conservation practices, how would it be possible to achieve these goals?” The answer was “only with a combination of practices, and only if every farm uses at least one of them.” This research began in 2010, using data about land use and farming practices from the previous five years (2006-2010), so the load reduction scenarios are relative to that “benchmark” period. The researchers later issued a supplemental report to compare the benchmark period to the baseline. Phosphorus went down due to changes in tillage but nitrogen went up due to an increase in corn and soybean acres and an increase in fertilizer application rates.
Using the information in ISU’s reports and dashboards, I’ve attempted to summarize our progress relative to both the baseline period (before the formation of the Hypoxia Action Task Force) and the benchmark period (before work began on the Iowa Nutrient Reduction Strategy).
Modeling vs. Monitoring
As I said, these are best-case scenarios. While we can certainly expect a big reduction in phosphorus pollution from the growth of no-till and cover crops, ultimately, the only way to be sure that water quality is improving in our rivers is to test it! If there’s a discrepancy between what you expect (a big reduction in phosphorus load) and what you measure (no clear trend in flow-weighted, five-year-moving-average phosphorus loads) that’s a sign that you left something important out of the spreadsheet! The most likely suspects are legacy sediment in the river valleys and livestock manure.
On the other hand, if your water quality data is incomplete or inconclusive or just hard to explain, it’s worth stepping back and asking yourself: “how big a reduction in nitrogen can I reasonably expect, based on the conservation practices installed so far?” If the answer is “1 or 2 percent,” there’s no need to wait for the results of a long-term study to acknowledge that your strategy isn’t working.
I remember doing that kind of reality check in 2019 for the Ioway Creek Watershed Management Authority, at the end of a four-year demonstration project. I did not enjoy being the bearer of bad news then, and I’m not enjoying it now. I remember how much work my colleagues put into those field days, and the ingenuity and vision displayed by the farmers who hosted them. I was there when the woodchips were poured into the first bioreactor in Boone County. So I totally understand the impulse to brag that Iowa now has 300 bioreactors, 3.8 million acres of cover crops, and 10.2 million acres of no-till. Many people worked hard to achieve those numbers! It is real progress! It’s kept nutrients and sediment out the water! It proves that there are many farmers who care about soil and water and are doing something about it! But it doesn’t prove that the Iowa Nutrient Reduction Strategy is working. For nitrogen, it definitely isn’t.
Conservation efforts have been partially offset by increased fertilizer use
I knew that we needed a lot more cover crops, wetlands, and saturated buffers to reach our nitrogen goal. Iowa Environmental Council has made this point with infographics. What I didn’t realize was the extent to which increases in fertilizer application rates have offset the hard-won gains that we’ve achieved so far.
Nutrient rate management was supposed to be the low-hanging fruit the Iowa Nutrient Reduction Strategy. At the time the INRS was written, the Maximum Return to Nitrogen (the point at which the yield bump from an additional pound of fertilizer doesn’t generate enough revenue to cover the costs) was 133 lbs/acre for corn in rotation and 190 lbs/acre for continuous corn. Reducing rates from 150 lbs/acre for corn in rotation and 201 lbs/acre seemed like an easy way to reduce nitrogen in the rivers by 10% while actually saving farmers money. Win-win! Instead, rates for corn in rotation averaged 173 pounds/acre for the past several years, which would raise nitrate levels in tile water by (roughly) 23%! Rates for continuous corn went down just a tiny bit, to 199 lbs/acre. What happened?
Several of the authors of the INRS science assessment just co-authored a new paper in Nature Communications which provides an answer. 133 lbs/acre was economically optimal under outdated assumptions about corn genetics and yield response, fertilizer and corn prices, and precipitation. Factoring all that in, the optimal rate for corn in rotation actually rose to 187 pounds/acre in 2020, leaving no opportunity for a win-win. Farmers are acting in their rational economic self-interest and applying as much nitrogen as is required to get good crop yields after a heavy spring rain. (Huge caveat: this doesn’t factor in manure). The researchers acknowledged that this is bad for water quality, as measured by a growing gap between the economically optimal rate and an “environmentally optimal rate” with some externalities priced in. Another way to say that: the fraction of agribusiness profits which come at the expense of other industries (i.e. commercial fishing in the Gulf, tourism for communities on polluted lakes) and the public (i.e. utility bills for customers of the Des Moines Waterworks, hospital bills for cancer patients) has been growing.
The companion piece to this paper is a new calculator. N-FACT uses data from on-farm nitrogen rate trials to factor in location, planting date, residual soil nitrogen, fertilizer price, and your best guess about corn prices and rainfall to provide a customized economically optimal nitrogen rate. The research that went into it is very impressive, and gave me a new appreciation all the factors that can influence agronomists’ recommendations and farmers’ decisions. I hope it will lead to reduced nitrogen losses by helping farmers improve their forecasting, but unless you’re doing a split application and soil or corn stalk testing, it seems like there’s still a lot uncertainty. Your optimal rate may vary by 40 pounds/acre depending on whether we get a wet spring or a dry spring. That’s why I’m more excited about Practical Farmers of Iowa N Rate Protection Program, which directly addresses uncertainty and risk.
What we really need is a calculator to answer the following questions about the Iowa Nutrient Reduction Strategy:
How much voluntary conservation will it take to offset future profit-driven changes in the industry?
How soon can we expect to see meaningful reductions in nitrate in our rivers and drinking water?
How many people will get preventable cancers in the meantime?
How long is the public going to put up with this before we demand a change in strategy?
What do I mean by “a change in strategy?” Making policy recommendations isn’t our wheelhouse, but if you’re looking for ideas, you might start with this 2020 op-ed by Matt Liebman, Silvia Secchi, Chris Jones, and Neil Hamilton, or this 2022 report by the Iowa Environmental Council.
In an interview with KCCI, Iowa Governor Kim Reynolds blamed the weather for high nitrate levels in the Raccoon and Des Moines rivers that led to an unprecedented outdoor watering ban for the Des Moines metro and dismissed any suggestion that Iowa needs to change its policies. Milli Vanilli’s 1989 hit “Blame it on the Rain” captures the vibe perfectly, so I covered the song and made a silly video with footage from the interview. However, the situation is no laughing matter.
Let me explain the situation as simply and clearly as I can. The high nitrate levels we are seeing this spring are not a fluke, drinking water is not completely safe in many communities across Iowa, and if we stay the course with Iowa’s Nutrient Reduction Strategy we will be waiting a long time for things to get better.
You can’t have it both ways
It’s true, nitrate pollution in rivers is influenced by both rainfall and recent drought. This has been a recurring theme in my analysis of water quality data (most recently here, and most rigorously here). But the Governor and her administration want to have it both ways. When nitrate in the Cedar River dropped due to favorable weather, they took that as a sign that a voluntary approach was working and took the unusual step of trying to withdraw a pollution budget that might have placed limits on new pollution from industry. Just last fall they were arguing that the following rivers should be removed from the Impaired Waters List, based on a 10% rule that makes no sense in the context of drinking water. The table below shows the data that they’re using to make those determinations.
Regardless of whether they meet the technical threshold for impairment, as a practical matter, the Raccoon River and Des Moines River regularly have nitrate levels high enough to cause problems for drinking water supply. The Central Iowa Water Works had to run their nitrate removal facility in 2024, 2022, 2019, 2018, 2017, 2016, 2015, 2014, and 2013. (This was reported recently by KCCI). It’s the largest such facility in the world, and this year it wasn’t enough!
Nitrate levels this spring are higher than average but not a fluke
The graphs below shows how daily nitrate concentrations and discharge (streamflow) in the Raccoon River this year compares to the median for that time of year. It is unusual for wet weather and high nitrate levels to persist through late July, but nitrate does exceed 10 mg/L about half the time in May and June. If you want to understand long-term nitrate trends in the Des Moines River and Raccoon River, read Chapter 5 of the new source water report commissioned by Polk County.
The Raccoon and Des Moines Rivers are not alone in having high nitrate levels this year. Here is 22 years of weekly data from a site on the South Skunk River, just downstream of Ames. This spring, peak nitrate levels (22 mg/L) were the highest we’ve seen since 2014. Average spring nitrate levels (15.5 mg/L) were the highest we’ve seen since 2015. However, it’s only a little above the long-term average (13 mg/L, indicated with a dotted black line) and ranks 7th out of 23 years for which we have data.
None of the data I’ve seen rules out a slight improvement in water quality in this or other Iowa rivers, masked by the ups and downs of an 8-10 year cycle. However the data does rule out this year being a fluke and us not having to worry about high nitrate levels in the future!
In Iowa, it’s normal for it to rain a lot in the spring. In watersheds with a lot of tile-drained farmland, it’s normal to see high nitrate levels for several days following a rainstorm. Ames is lucky to have a buried sand-and-gravel aquifer with the right geology and chemistry to remove most of the nitrogen before it reaches wells. If we withdrew water directly from the Skunk River, it would exceed the drinking water standard every year. Many other communities in Iowa are not as fortunate in their geology.
Nitrate in Drinking Water Poses a Widespread Health Risk
The Safe Drinking Water Act was written so that we must draw a hard line between “safe” and “unsafe.” Drinking water utilities must meet a Maximum Contaminant Limit of 10 mg/L nitrate as nitrogen. Most large water systems have been able to say on the “safe” side of the line, although it can be costly to do so. However, the standard hasn’t been updated to reflect research on the link between chronic exposure to nitrate in drinking water and various cancers. And really, it’s better to think of health risks as a continuum from “more safe” to “less safe.” The Environmental Working Group created a map a few years ago showing which communities fall in the “not as safe as they could be” range for nitrate in drinking water. Last year, Iowa Environmental Council recently released a report about the health risks of nitrate in drinking water and is now hosting a series of listening sessions on cancer and the environment.
Conservation efforts have been partially offset by increased fertilizer use
Shouldn’t we expect some improvement in nitrogen levels due to the state’s nutrient reduction strategy and the conservation efforts of farmers? I’ve written another article to dig into this question but the short answer is that we can expect at most a 2% reduction in nitrogen losses over the past decade. That’s for the state as a whole, some watersheds are doing better or worse and we don’t have a good tracking system to evaluate it. Most of the progress that we can expect from cover crops and nitrification inhibitors have been offset by increases in fertilizer application rates, which apparently made economic sense to do.
I can’t really blame farmers for acting in their economic self-interest. I do think it’s fair to blame your elected officials if they can’t take drinking water safety seriously and offer better solutions. Just don’t blame it on the rain.
Testing multiple sites within a short time period can provide a “snapshot” of water quality across a watershed, county, or state.
Polk County Conservation had great turnout for their spring water quality snapshot on May 20, testing 117 sites! I scheduled our event for the same day and volunteers help me test another 45 sites in Story, Boone and Hamilton counties. We also did some follow-up testing on May 21 for quality control and collected water samples for the lab. I have assembled the results from both events into a colorful interactive map that shows where water quality was good, fair, or poor in central Iowa during those two days.
There were a lot of “poor” readings on May 20. Not only was nitrate in the Skunk River and Raccoon River higher than we’ve seen in a decade, the water in most creeks was chocolate brown with sediment and had E. coli counts in the thousands.
One reason we do snapshot events is to get a better sense for where that pollution is (and isn’t) coming from. You’ll notice that streams with urban watersheds like Yeader Creek in Des Moines and College Creek in Ames have much lower nitrate than streams in rural areas. However, urban streams had high levels of sediment and fecal bacteria.
The other reason we do snapshot events is to provide a hands-on educational experience for people who might be curious about water quality but who can’t commit to monitoring a stream twice a month. I joined six classes of earth science students (taught by Kean Roberts and Collin Reichert) to test sites within walking distance of Ames High School. While there were a few complaints about the weather and walking in heavy waders, most students enjoyed the break from the classroom and spotting wildlife. The data students collected is part of a larger citizen science effort.
Volunteers in the Ioway Creek watershed have been doing twice-a-year snapshot events since 2006. Prairie Rivers of Iowa helped keep the tradition going after the IOWATER database was shut down in 2017, and we are in the process of uploading the data from those events to a permanent home on the Izaak Walton League’s Clean Water Hub!
However, I’ve wondered whether we should keep doing these events the same way now that Story County Conservation staff and volunteers are testing many of these streams on a regular basis. This is the third map I’ve made from a coordinated snapshot event (see also May 2024 and September 2023) and I’ve noticed some issues with our standard suite of tests that limit our ability to narrow down where pollution is coming from or where conservation practices are making a difference:
Nitrate test strips are not very precise at the high range (color matches at 10, 20, or 50 mg/L). This can be improved with a smartphone app. We also had some big discrepancies that we traced back to a bottle of just-expired strips that I had assumed would still be okay; when in doubt, throw them out!
Dissolved oxygen in streams has a daily cycle (rising in the afternoon when plants and algae are photosynthesizing), so sampling at the same time of day is more important than sampling on the same day.
During scattered showers, water clarity may not tell us where the soil is better protected from erosion, just where the rain was more or less intense.
It’s difficult to match colors to get a phosphate reading when the water is cloudy with sediment. I’ve tried filters but they clog with silt before you can get a 25 mL water sample.
Our next volunteer monitoring event might look a little different. I’d welcome ideas for how we can collect more useful data or get more new people involved!
I’m sharing some vacation photos, taken at the Athabasca Glacier in Alberta, Canada, because it’s a nice window into Iowa’s icy past and its warming future. Earth science concepts like glacial moraines and watersheds and climate change that can be subtle or hidden in Iowa are plain to see in the mountains!
1. Glacial Ice
This is the Athabasca Glacier. It’s a slow moving river of ice 4 miles long and 300-980 feet thick, sliding off the larger Columbia Icefield in the Canadian Rockies. It looks big from a distance, and it feels even bigger when you’re walking across it on crampons and aren’t used to the altitude! The depth of the ice became apparent when we looked into a crevasse.
All of Iowa looked like this at some point during the last 2 million years, except the ice was even thicker. The Des Moines Lobe of the Wisconsinian ice sheet melted from northern and central Iowa just 12,000 years ago, leaving behind flat, marshy land. Other parts of Iowa have been ice-free for longer and had more time for wind and water to shape the hills and valleys.
2. Glacial Till
A sheet of ice hundreds of feet deep is heavy, and pushes against the earth with tremendous force as it slides slowly downhill. This photo shows both the scratches on the bedrock made by the glacier and the glacial till that it leaves behind–an unsorted mix of sand, silt, gravel, and boulders. You don’t have to travel to the Canadian Rockies to see Canadian rocks; during the ice age, the glaciers carried some all the way to Iowa!
Like a bulldozer, glaciers smooth out the ground underneath and leave a big pile of material at the edge when they stop. That’s why there’s a line of hills near Des Moines and a lot of flat land north of there. You can see a flat ground moraine in the foreground of this picture and a steep lateral moraine in the background.
3. Soil Formation
Despite the harsh conditions at the edge of the glacier, a few tiny flowers were blooming! This plant is a Saxifrage, “stone-breaker” in Latin. Plant roots and associated fungi speed up the process of breaking down rock and turning it into soil.
It’s still a slow process! It took thousands of years for prairie roots, microbes, and burrowing animals to turn lifeless glacial till into Iowa’s rich black topsoil, but only 160 years of tillage to lose half of it. Fortunately, there are ways to grow crops without degrading our soil. As Practical Farmers of Iowa puts it, “don’t farm naked!”
4. Continental Divide
The Columbia Icefield sits at the junction of two continental divides. Meltwater from the Athabasca Glacier joins the Saskatchewan River, which ultimately makes its way to Hudson Bay. However, meltwater from the Stutfield Glacier on the other side of the mountain ends up in the Arctic Ocean, and meltwater from the Columbia Glacier goes to the Pacific Ocean.
In the Canadian Rockies, the watershed boundaries are impossible to miss: lines of awe-inspiring mountain peaks on either side of a river valley. You might be driving along the Bow River until you reach it’s headwaters, and then you come to a mountain pass, your ears pop, and… ta da! You’re in a new watershed, following the Mistaya River downhill.
In Iowa, the dividing lines between land that drains to the Mississippi River and the Missouri River (or any other pair of rivers) are hard to find without a topographic map. We’ve put up watershed signs around Story County to make it more obvious.
Why does is matter what watershed you’re in? Well, knowing which land drains to which river can tell you something about the water quality in the river, and who to talk to if you want to improve it.
5. Meltwater
Our guide refilled our water bottles from a stream of glacial meltwater. I felt comfortable drinking it without boiling or filtration because nothing lives on a glacier. Elsewhere in the mountains, there’s a risk that wild animals living in or near the water might have left behind a little present containing a parasite like Giardia. Fecal contamination tends to get worse as you move downstream into areas with a lot of cows or a lot of people, and Alberta has its own set of water quality issues associated with mining and oil extraction. However, there’s a notable difference from Iowa: when natural resource agencies issue a beach advisory because of E. coli, it’s unusual enough to make the news!
The water from the glacier was refreshing but tasted a little… dusty. Like the taste in your mouth when you’re standing on a gravel road and truck passes by. Ames tap water is better!
However, the glacial dust (rock flour) reflects the light, turning mountain lakes a lovely shade of blue, turquoise, or green. In Iowa, green or blue-green colored water is usually a sign of an algae bloom, unpleasant to swim in and possibly toxic!
6. Climate Change
We made sure to include a visit to the glacier in our vacation plans because there may not be many more opportunities to see one. In a stable climate, a glacier would melt a bit in summer and grow back with winter snows. In a warming world, glaciers are melting rapidly.
Driving from the visitor center to the trailhead, we passed a series of ridges (terminal moraines) marked with dates. Since 1844, the ice has been receding and the pace of melting has accelerated in recent years. None of my pictures capture this, so I will screenshot an a pair of images from the Mountain Legacy Project and point you to Amy Snider for more art, maps, and photos about the Athabasca Glacier.
Climate change has been less noticeable in Iowa than in other parts of North America because of the moderating influence of corn sweat (evapotranspiration), but that won’t last. Rising temperatures, more intense spring rains, and greater weather variability are projected to lower yields and undermine what little progress we’ve made in addressing water quality. Alberta’s economy is dependent on fossil fuels, but Iowa has a lot of gain from a transition to green energy, and a lot to lose if we don’t make the switch.
7. Fossils
At the edge of the glacier, we saw a trilobite fossil in a 510-million year old rock, a relic of a time when erosion rates were even higher than they are now because there weren’t any plants yet. The broken shells, sand, and silt that covered the seafloor has since turned to rock and been pushed up to form new mountains.
The trilobites are long gone, wiped out during another episode of global warming and ocean acidification, this one triggered by massive volcanic eruptions 252 million years ago. It was the biggest mass extinction in Earth’s history, but after fifty million years or so, the land, seas and sky were teeming with new species.
If you take a long enough view, arable soil, clean water, and biodiversity are renewable resources. On human timescales, they’re definitely not. Agriculture and civilizations developed during a time of stable climate, and they may not last much longer if we don’t take more aggressive action to limit greenhouse gas emissions. The Earth will go on without us.
There is poop in Iowa’s lakes and rivers! I’m sure you know this by now. The Iowa DNR monitors bacteria at 39 beaches every week during the summer and posts a “swimming not recommended” sign if the average for the month exceeds 126 E. coli/100mL. If a lake has a history of problems, another threshold (235 E. coli/100mL in a single sample) is used as an early warning system. As Iowa Environmental Council has reported, Iowa DNR issued 134 of these beach advisories last summer. Streams are monitored less often, but we can use the same thresholds to evaluate average conditions at the end of the season. Last year, all 15 streams that we monitor in Story County had E. coli levels above the primary contact recreation standard.
Story County Conservation posted a warning sign at the Tedesco Environmental Learning Corridor.
Okay, but what do we do with that information?!
I know some people who are so grossed out they won’t dip their toes in any lake or river in Iowa, even if the DNR says it’s okay. I know some other people who went ahead with a canoe trip on the Des Moines River, despite reports that just two days before, a broken sewer main in Fort Dodge had released 400,000 gallons of raw sewage into the river upstream of their route. They’ve paddled polluted waters before and figured it was no worse than usual.
Part of the difficulty is that some people translate “an unacceptably high number of beach advisories” to “lots of poop in the water everywhere all the time.” That’s not what’s happening. If you picked a summer weekend and a state park at random, and took your family to the beach, you would have had a 77% chance of swimming in water that met the primary contact recreation standard. If you subscribe to IEC’s Water Watch newsletter, you can make sure you pick the right one!
Part of the difficulty is that Iowa relies heavily on just one threshold to issue alerts and place waters on the Impaired List. Some other states have started used a red/yellow/green warning system that distinguishes between “swimming not recommended” at 235 E. coli/100mL and “beach closed” at 1000 E. coli/100mL. This is helpful if you’re a little more tolerant of risk or are doing activities that will keep your head above water. That upper limit is the same as the one used during the 2024 Summer Olympics to determine whether to hold swimming events in the River Seine.
Seine River in Paris, photo credit Erik Larson
You may recall that Paris spent $1.5 billion to clean up the Seine River in time for the 2024 Summer Olympics and still had to postpone some events because of poor water quality. Similarly, Story County Conservation has spent $3.4 million to restore Hickory Grove Lake and still had to post beach advisories four weeks last summer. There is no easy fix for these problems. However, a long-term perspective on water quality in the Seine shows how an open sewer can become a swimmable river (at least most of the time) with improvements in wastewater treatment. Yes, Iowa has more livestock than people, but I’ve been seeing some evidence that points to humans as the main source of feces and pathogens in many of Iowa’s waterways. If that’s true, then our water quality could benefit from projects to replace combined sewer systems (we still have a few), add liners to rusty sanitary sewers, get septic systems up to code, and make some overdue upgrades to sewage treatment plants.
Randy Evans was on the right track when he compared water quality in Iowa to water quality in Paris, but he only looked at one day. I’ve gone a few steps further. In the attached table, I’ve shown the best, worst, and average E. coli readings measured last year at some of Iowa’s most popular beaches and water trails. Below, I’ve put them in broad categories, benchmarked to some examples from France. I’ve also included some sites we monitor in Story County, in bold. Get ready to calibrate your disgust!
How do we measure poop in the water?
Escherichia coli is a species of bacteria found in the guts of birds and mammals. Some strains are harmless and some can put you in the hospital. It’s an easy-to-measure proxy for feces in the water, which could carry a wide variety of disease-causing microbes. E. coli can be measured directly by counting dots in a Petri dish (Colony Forming Units, CFU/100mL) or indirectly using a chemical reaction (Most Probable Number, MPN/100mL) but the results are similar enough that these units are often used interchangeably.
Typical laboratory protocols have a lower detection limit of 10 and an upper quantification limit around 24,000. With such a big range, E. coli data has to be plotted on a log scale and averages have to be expressed as a geometric mean or median—basically, worry less about the exact number and more about the number of digits.
1 digit: As clean as it gets without chlorine
Too low to detect, with typical methods (reported as <10)
A typical beach day at Peterson Park
A typical beach day at Lake Rathbun, Gray’s Lake, or Lake Okoboji
A good day at most lakes on the impaired list
Peterson Park Beach. A favorite spot for my family during COVID lockdown and consistently clean.
2 digits: Have fun in the water!
Meets Iowa’s primary contact recreation standard (geomean <=126, single sample <=235)
A typical day at a French stream running through forest or cropland
Treated effluent from Iowa sewage treatment plants with UV disinfection
A typical beach day at Hickory Grove Lake
A typical beach day at Lake MacBride (Iowa City) or Big Creek
A bad beach day at Peterson Park
A bad beach day at Lake Okoboji
A typical day at the Charles City or Manchester whitewater parks
A good day at most rivers on the impaired waters list
Kayaker at Manchester whitewater park. I tipped and swallowed water when I attempted it, but it was probably fine.
Low 3 digits: Swim at your own risk (families)
May exceed IA primary contact recreation standard (geomean >126, single sample >235)
A typical day at a French stream running through pasture
The Seine River in Paris during the women’s marathon swim
A typical beach day at Clear Lake or Lake Darling
A bad beach day at Lake Rathbun
A bad day at the Charles City whitewater park
A typical day on the S. Skunk River water trail
Kids swimming at Clear Lake. No beach advisory on this day, but there had been other weeks.
High 3 digits: Swim at your own risk (athletes), canoe at your own risk (families)
May exceed Iowa’s secondary contact recreation standard (geomean > 630, single sample >2,880)
The Seine River in Paris during the men and women’s triathlon
A typical day at Ioway Creek in Ames
A typical day on the lower Maquoketa River (near Spragueville)
My daughter playing on a sandbar in Ioway Creek in Ames. I’m sad to say it, but I don’t think kids should be playing in this water.
4 digits: No swimming, canoe at your own risk (experienced paddlers)
Action limit for beach closures in some states (single sample > 1000)
A bad day for the Seine at the 2024 Olympics; men’s triathlon postponed
A typical day for the Seine in the early 2000s (since improved sewage treatment, but before sewer system improvements)
Treated effluent from modern Paris sewage treatment plants
A bad beach day at Gray’s Lake, Lake MacBride, Big Creek, Clear Lake, or Lake Darling
A typical day at West Indian Creek, downstream of an outdated sewage treatment plant
A bad day on the Skunk River or Ioway Creek (1.5 inch rain previous night)
A bad day at the Manchester whitewater park
Canoe trip on Ioway Creek in Boone County. I collected a water sample at this moment. E. coli measured 2,390 CFU/100mL.
5-6 digits: Stay out of the water
May be too numerous to count, with typical methods (reported as > 24,000)
A typical day for the Seine in the 1980s, before modern sewage treatment
A bad day on the Seine River in 2008, before attempts to control combined sewer overflows
A bad day at West Indian Creek (1.5 inch rain previous night), downstream of an outdated sewage treatment plant
Flash flooding in the Skunk River or Ioway Creek (June 2022). No one should be in the water during these conditions.
Two bad days on the lower Maquoketa River (near Spragueville), during high water levels
A bad day at Hickory Grove beach. Previous studies have shown that the main source of the bacteria is geese and dogs at the beach.
The new Nevada sewage treatment plant should be operational this year and will have a UV disinfection system like this one. This should make it safer for kids in Maxwell to play in Indian Creek.
Cracked sanitary sewer in Ames leaking into Ioway Creek, September 2009
No picture for this one. You’re welcome!
What is the risk of poop in the water?
Recreational water quality standards are based on epidemiological studies at swimming beaches. Researchers have found that swimmers were more likely than non-swimmers to get sick with gastroenteritis (“stomach flu”) and that illness rates were higher at beaches with more fecal indicator bacteria. Symptoms can range from mild to dangerous and are often falsely attributed to food poisoning. The EPA recommended a threshold of 126 E. coli/100mL to keep the risk of illness below a certain level for swimming, water skiing, children’s play, and other “primary contact” activities, but you should think of it as a point on a continuum rather than sharp break between “safe” and “unsafe.” Secondary contact recreation standards are used less often and involve some adjustment factors.
There are many factors that can influence whether you get sick while at the beach—how much water you swallow or get on your face, whether the source of the feces is human or animal, your general health, and previous exposure to the pathogens. There are also some challenges in accurately quantifying E. coli levels in water, which can vary a lot even within the same body of water and over a short period of time. I ran across a randomized control trial from Germany that controlled for all these factors. Some 2000 people were recruited to spend an afternoon at one of four locations (3 lakes and 1 river). Half stayed on shore and half were asked to spend ten minutes in the water, dunk their head at least three times, and report if they accidentally swallowed water. Water samples were collected every 20 minutes from the center of the swimming area and tested for E. coli. Researchers tracked how many people got sick over the next week with symptoms of a waterborne illness. Here are the results.
Water quality (E. coli/100mL), by quartile
Incidence rate of gastroenteritis
Control group
2.8%
0 to 72
1.9%
72 to 181
5.2%
181 to 379
6.6%
379 to 4,600
8.2%
What about really polluted water? An academic review board would never approve an experiment to send 931 people into a bay polluted by a combined sewer overflow, but a group of Danish triathletes was reckless enough to do it for fun. After swimming 3.8 km in water with an estimated 15,000 E. coli/100mL, 42% of them got sick with Campylobacter, Giardia, or E. coli!
There you have it, these are ballpark, intuitive judgements about when to go in the water and when to stay out, but they are informed by good science. Oops, did I just give health and safety advice without running it by anyone?
Prairie Rivers of Iowa is not a medical professional and our work is not conducted under a DNR-approved quality assurance plan, please consult your doctor and refer to section 567-61.3(3) of the Iowa Code, terms and conditions apply.
Bottom line, you may disagree with the interpretation I’ve outlined here, but there’s clearly a lot of wiggle room to enjoy Iowa’s waters without taking unnecessary risks with your health.
