Swim warnings on track to eclipse previous years

Iowa's state beaches are likely to be deemed unsafe for swimming more times this year than the seven previous years amid abundant rainfall and high heat, according to Iowa Department of Natural Resources data.

So far this year, 111 weekly warnings have been issued about unsafe concentrations of bacteria and of algae toxins in the water near the beaches. The state monitors about 40 of them between Memorial Day and Labor Day, when swimming is most common.

The number of warnings already has eclipsed some recent years, and three weeks are left in the 2024 monitoring season.

“We are definitely on track to get well over the last few years,” said Alicia Vasto, water program director for the Iowa Environmental Council, which tracks the warnings. “That's a good indicator that we're not making improvements.”

Unsafe concentrations of bacteria and toxins can cause skin irritation, infections and illness.

Several factors can affect those concentrations, but week-to-week changes in the sheer amount of bacteria is often tied to rainfall because it washes fecal matter from geese and other creatures into the water.

The toxins frequently result from large algae blooms — when the microorganisms grow rapidly and blanket the water's surface — that occur during calm and hot conditions.

Farm runoff also affects the lake water. Nutrients in fertilizer and manure can feed algae blooms.

Backbone, Beeds lead

The beach water that has been the most persistently unsafe for swimming this summer has been at Backbone State Park in Delaware County, about 40 miles north of Cedar Rapids, and Beeds Lake State Park, near Hampton in north-central Iowa. Both have had swim warnings for 10 of the past 12 weeks.

The warnings for those beaches have been tied to high bacteria concentrations. In one of the tests, Backbone water had a concentration that was 85 times the amount that can trigger a warning.

At Lake Darling State Park in Washington County, about 50 miles south of Cedar Rapids, unhealthy amounts of algae toxins have been reported for four weeks.

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The Pleasant Creek State Recreation Area near Palo has had bacteria warnings for the four most recent weeks.

The number of weekly swim warnings has increased substantially since early June, when there were none. In the past month, there have been at least a dozen at any given time, with a high of 17 last week. This week, 14 warnings were issued.

“As the summer progress, things get hotter,“ said Dan Kendall, the state’s lake and beach monitoring coordinator. “As the sand heats up near that water interface, you can definitely create a better incubator where bacteria tends to replicate faster.”

This year to date has been the state’s eighth wettest and ninth warmest on record, according to Iowa State University data.

Kendall said the DNR continues to study why certain lakes have consistent — or inconsistent — problems with bacteria and toxins. Recently, that has included sampling deeper lake water to see whether lurking nutrients might be occasionally circulated to the surface, which could explain the apparent inconsistencies, Kendall said.

“Any one system can just bloom — and it can be persistent for a year — and another year there might not be any,” he said.

Comments: (319) 368-8541; jared.strong@thegazette.com