Green Stuff in the Skunk River

Green Stuff in the Skunk River

On Tuesday, March 12, residents on the north edge of Ames noticed that the South Skunk River was cloudy and had turned an unusual shade of bluish green.  By the time I looked at it on the afternoon of March 13, the color had faded and the water was less cloudy, but it still had a soupy, streaked appearance that I’ve seen before in lakes following a toxic algae bloom.  I’m gonna go out on a limb here and say it’s blue-green algae (cyanobacteria).

Cyanobacteria bloom in the South Skunk River
Cyanobacteria bloom, showing paint-like streaks.
Cyanobacteria bloom in the South Skunk River.

“Algae” is a word that gets lazily applied to any living thing that does photosynthesis but that isn’t a plant: from tiny glittering diatoms in a drop of pond water to giant kelp in the oceans.  The other kind that I noticed in the South Skunk River this week is filamentous green algae, which forms slimy hair-like strands on rocks and globs on the water’s surface.  Color is the least of the differences.

Cyanobacteria are tiny and simple.  There’s strong evidence that the chloroplasts in the cells of plants and green algae are the captured descendants of cyanobacteria. This amazing phenonemon is called endosymbiosis, and it’s happened multiple times in the history of life on earth.  If you’ve never heard of it, I’d recommend this YouTube video, which explains the concept with cartoons.

The practical reason to know if the green stuff in the water is cyanobacteria is because they can produce toxins.  I wasn’t able to get a sample tested for microcystin (and chances are, this algae bloom will have dispersed by the time you read this), but I would recommend keeping your dog out of water that looks like paint or pea soup, to be on the safe side.

Green algae in the South Skunk River (Rick Dietz)
A simple guide for green stuff in the water.

Why is the water so green, so early?  Algae growth is limited by the availability of light, heat, and fertilizer–phosphorus in freshwater, and to a lesser extent nitrogen.  We’re getting unseasonably warm weather before there’s any leaves on the trees to shade the water.  As for the fertilizer, I’m not sure where it came from, or when.  Rick Dietz and I tested nitrate and phosphate with field kits on Wednesday and measured 0 mg/L.  Nitrate and phosphorus levels were also fairly low at this site when we collect grab samples in February.  Maybe something was washed into the river earlier in the week, but it has since been used up by the algae or has washed downstream.  I’ll amend this article if I find out something conclusive.

Green Stuff in the Water

Green Stuff in the Water

I got a good look at a cyanobacteria “bloom” over Labor Day weekend, at a lake in Wisconsin.  Cyanobacteria can produce toxins, and this proliferation of green gunk had done so earlier in the month, causing a large number of fish to go belly up.  Cyanobacteria toxins can also be dangerous for people and dogs.

There were warning signs posted but they were wordy and left some doubt about whether it was okay to go in the water. Some kayakers were ignoring them.  This has been an issue in Iowa as well.  The Iowa Environmental Council is working with Iowa DNR to make the warning signs simpler and more visible.  The Environmental Working Group recommends that midwestern states do more frequent testing for microcystins, the most worrisome class of cyanobacteria toxins.  I support these steps, but I also think it’s important to let the public know what to look for, as its not always possible to run tests and post warnings in a timely manner.   How about this rule of thumb, illustrated in the graphic above?  If it looks like paint, stay out! 

Not every cyanobacteria bloom can be so easily identified, and not all cyanobacteria produce toxins, but enough of the toxin-producing species do look like spilled paint or “pea soup,” that it seems like a good starting point.

When I first arrived at the lake, it was streaks of green and brown in the water, like the rinse station for a child’s art project. The next day, more had been blown to our side of the lake and it formed a thick surface scum with bubbles, like latex paint left out for too long, and had a nasty smell.  The color was a bright green mixed with brown but cyanobacteria blooms can also be bluish green, blue, brown, or red.

Some of the harmless green things more commonly growing in lakes, streams, and ponds look completely different, as pictured above.

Duckweed looks like confetti scattered on the water surface.  There’s a few different species ranging from dots (the 1 cm Spirodela) to specks (the 2 mm Wolffia).  They are large enough you see the individual round leaves with the naked eye, and they sometimes have trailing roots. Surprisingly, it’s actually a flowering plant related to peace lillies, with tiny, wind-pollinated flowers. As the name implies, they are an important food source for waterfowl.

Green algae are a huge assortment of plant relatives, some single-celled and microscopic (until there are enough to turn the water green), some joining together into spheres, nets, or filaments.  Filamentous green algae look like slimy hair when they grow on rocks, and like drain clogs when they are dislodged and float on the surface or wash up on beaches.

And then there’s a variety of aquatic plants (pondweeds, coontail, and others) that can be found rooted to the bottom.  While dense “weeds” can be a nuisance for motor-boaters, a plant-dominated lake is better for fish than an algae-dominated lake, or one with nowhere to hide and nothing to eat.

If the lake looks like paint, stay out! Experts, can I say that?  It’s an over-simplification, but not everyone has the patience to read a more complicated message, or the good sense to take it seriously.

For more on harmful algae blooms and how to keep yourself and and your dog safe, the Iowa Public Health Department has some good resources.