Prolific bacteria, toxins detected at Spirit Lake beach

By: - August 22, 2022 5:07 pm

Algae blooms can happen on Iowa lakes when the water is warm and calm. (Photo by Perry Beeman/Iowa Capital Dispatch)

The water at a Spirit Lake beach recently had the highest concentrations of bacteria detected so far this year at any state beach in Iowa and also an unhealthy amount of blue-green algae toxins, according to the Iowa Department of Natural Resources.

Crandall’s Beach water last week had more than 100 times the amount of E. coli bacteria than the concentration that typically can trigger warnings about swimming at state beaches.

“This is the first one that the test kit has gotten maxed out on this year,” said Daniel Kendall, the DNR’s lake and beach monitoring coordinator.

That means the DNR’s weekly test revealed more than 24,000 viable bacteria in less than a half cup of the lake water. The tests are unable to quantify the number of bacteria above that level.


In Iowa lakes that are prone to unhealthy concentrations of bacteria, a single test that detects 235 viable bacteria can prompt the DNR’s “swimming not recommended” warning.

Crandall’s Beach is classified by the state as “less vulnerable” to the unhealthy conditions. It has averaged about 27 viable bacteria per 100 milliliters in its last five samples.

Bacteria concentrations in Iowa’s lakes can shift dramatically over the course of days, which is why the DNR samples state beaches once each week during warmer months when people are most likely to come in contact with the water. The department maintains a map that shows the beaches that have elevated amounts of bacteria and toxins that can cause skin irritations, illnesses and infections.

Kendall said there are many factors that can affect bacteria growth in Iowa’s lakes, and that it’s difficult to pinpoint a culprit for the situation at Crandall’s. But here’s one scenario:

Spirit Lake has a fairly significant blue-green algae bloom right now near the beach that stretches into the lake for perhaps 50 yards, Kendall said. That’s the source of the toxin warning at the beach.

The cyanobacteria that causes those “blooms” — or overgrowths — was likely multiplying during the series of heat waves that torched western Iowa this summer. The microorganisms like to feast on farm fertilizer runoff when the water is hot and calm.

Then the wind pushed all those cyanobacteria that drift near the water’s surface to the northwest corner of the lake where Crandall’s Beach is located. Marble Beach is a bit south of there, and it had elevated toxins, too, but far fewer E. coli. On the opposite side of the lake at Orleans City Beach, there were no detected toxins and just 10 viable bacteria per 100 milliliters of water.

Parts of the bloom have turned a bright blue, indicating the cyanobacteria is running out of food and dying, and they become a food source for E. coli.

Spirit Lake has also had about 3.8 inches of rain this month, said Samantha Trellinger, a National Weather Service meteorologist. That’s about 40% more than normal.

That rainfall likely washed E. coli bacteria into the lake, including from the feces of geese that could be more likely to collect on the beach because people are avoiding the smelly algae bloom.

“If I’m coming up on that, I’m not going in that water,” Kendall said.

The DNR will test the water at the beach again on Wednesday. Kendall predicts the bacteria counts and toxin concentrations will still be too high for safe swimming. The DNR publishes the results of those tests on Fridays.


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Jared Strong
Jared Strong

Senior reporter Jared Strong has written about Iowans and the important issues that affect them for more than 15 years, previously for the Carroll Times Herald and the Des Moines Register. His investigative work exposing police misconduct has notched several state and national awards. He is a longtime trustee of the Iowa Freedom of Information Council, which fights for open records and open government. He is a lifelong Iowan and has lived mostly in rural western parts of the state.