Calibrate Your Disgust

by Dan Haug | Apr 11, 2025

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.

Water quality notice at TELC — 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

Kids playing at Peterson Park beach — 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 — 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
Treated effluent from outdated Iowa sewage treatment plants (Osceola, Nevada, Knoxville, LaPorte City)
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.

UV disinfection at Ames WPCF — 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.

7-8 digits: Raw sewage or manure

Untreated wastewater entering Parisian sewage treatment plants
Combined sewer overflow in Paris
Hog manure spill in creek near Bloomfield, 2021
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.

Can Infrastructure Spending Help Iowa’s Polluted Rivers?

by Dan Haug | Jan 1, 2024

The display department for the plans. If you've read Douglas Adams, you'll appreciate the joke.

“But look, you found the notice didn’t you?”
“Yes,” said Arthur, “yes I did. It was on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying Beware of the Leopard.”

– Douglas Adams, The Hitchhiker’s Guide to the Galaxy

I was reminded of this scene after spending a long day cross-referencing the Raccoon River TMDL (a pollution budget for nitrate and E. coli) with permits and monitoring data for wastewater treatment plants. In this case, I suspected that polluters were getting away with something, but I’ve had just as much trouble finding information when I wanted to document a success story.

Effluent limits for nitrogen are not strict. Wastewater treatment plants and meatpacking plants in the Raccoon River watershed routinely discharge treated wastewater with nitrate 4-6x the drinking water standard. Why is this allowed? The 2008 Raccoon River TMDL capped pollution from point sources at the existing level, rather than calling for reductions. Due to limited data, the wasteload allocations were an over-estimate, assuming maximum flow and no removal during treatment.

That’s all above board, but someone else at the DNR went a step further. Wasteload allocations in the TMDL were further inflated by a factor of two or three to arrive at effluent limits in the permits, using a procedure justified in an obscure interdepartmental memo. The limits are expressed as total Kjeldahl nitrogen, even though the authors of the TMDL made it clear that other forms of nitrogen are readily converted to nitrate during treatment and in the river. In short, the limits in the permit allow more nitrogen to be discharged than normally comes in with the raw sewage!

For example:

The Storm Lake sewage treatment plant has an effluent limit of 2,052 lbs/day total Kjeldahl nitrogen (30-day avg). Total Kjeldahl nitrogen in the raw sewage is around 1000 lbs/day.
The Tyson meatpacking plant in Storm Lake has an effluent limit of 6,194 lbs/day total Kjeldahl nitrogen (30-day avg). Total Kjeldahl nitrogen in the raw influent is around 4,000 lbs/day.
I also checked a permit affected by the (now withdrawn) Cedar River TMDL. Same story. The Cedar Falls sewage treatment plant has an effluent limit of 1,303 lbs/day total nitrogen (30-day avg). Average total nitrogen in the raw sewage is between 1000-1500 lbs/day.
Confused about the units? That may be deliberate. Total Kjeldahl nitrogen includes ammonia and nitrogen in organic matter. Nitrogen in raw sewage is mostly in these forms, which need to converted to nitrate or removed with the sludge in order to meet other limits and avoid killing fish. Nitrogen in treated effluent is mostly in the form of nitrate. At the Tyson plant, the effluent leaving the plant has around 78 mg/L nitrate, versus 4 mg/L TKN, but figuring that out required several calculations. At smaller plants, the data to calculate nitrate pollution isn’t even collected.

As part of the Iowa Nutrient Reduction Strategy, large point source polluters are supposed to evaluate the feasibility of reducing nitrate to 10 mg/L, and phosphorus to 1 mg/L. Tyson did a feasibility study for phosphorus removal, and is now adding new treatment to its Storm Lake plant. However, it is not required to evaluate or implement further nitrogen reduction, “because it is already subject to a technology-based limit from the ELG.” This federal Effluent Limitation Guideline was challenged in court by environmental groups this year, and is now being revised by the EPA. It allows meatpacking plants to discharge a daily maximum of 194 mg/L total nitrogen!

Fortunately, all this creative permitting has little impact on the cost and safety of drinking water in the Des Moines metro. According to research in the TMDL, point sources only account for about 10% of the nitrogen load, on days when nitrate in the Raccoon River exceeds the drinking water standard. However, the figure is much higher (30%) for the North Raccoon River. I started looking at permits and effluent monitoring because I was trying to explain some unusual data from nitrate sensors, brought to my attention by friends with the Raccoon River Watershed Association. During a fall with very little rain (less than 0.04 inches in November at Storm Lake), nitrate in the North Raccoon River near Sac City remained very high (8 to 11 mg/L). The two largest point sources upstream of that site can easily account for half the nitrogen load during that period.

I was glad to be able to solve a mystery, and hope that this investigation can lead to some tools and teaching materials to help others identify when and where point sources could be influencing rivers. The load-duration curves in the 200-page Raccoon River TMDL are very good, but some people might benefit from something simpler, like this table. In general, the bigger the facility, the smaller the river, and the drier the weather, the more point sources of pollution can influence water quality, and the more wastewater treatment projects can make a difference.

Spreadsheet for estimating impact of wastewater.

I made this table to estimate how biological nutrient removal in Nevada and Oskaloosa (about 1 MGD each) could improve water quality in the South Skunk River (about 1000 cfs on average near Oskaloosa, but there could be greater benefit in tributaries, or when rivers are lower).

In this work, I’m supported by partners around the state and a grant from the Water Foundation. The project (Movement Infrastructure for Clean Water in Iowa) focuses on building connections and shared tools around water monitoring, and will continue through this spring and summer. The funders’ interest is in helping the environmental movement make the most of the “once-in-generation opportunity” presented by the Inflation Reduction Act and the Bipartisan Infrastructure Law. This fiscal year, the Bipartisan Infrastructure Law is adding $28 million to Iowa’s Clean Water State Revolving Fund, which provides low-interest loans to communities to replace aging sewer systems and treatment plants. Can that infrastructure spending help Iowa’s polluted rivers? We won’t know for sure without better use of water quality data, and greater transparency in state government.