Which Iowa beaches are unsafe for swimming on July 4?

If your holiday plans include a dip in a nearby lake, here is some good news: Most of Iowa’s state park beaches this week have water quality within safe standards for swimming.

Backbone State Park Ranger Jeff Hildebrand has been enjoying telling staff and visitors the lake at the park near Dundee in Northeast Iowa hasn’t had a no-swim warning yet this summer.

“People ask about the sampling results and I’ve been telling them its coming back clean,” Hildebrand said Monday. “A lot of it might be lack of rainfall, but even with some of the recent rain we’re staying clear.”

The Iowa Department of Natural Resources collects water samples each week at state park beaches and tests the water for E. coli bacteria and toxins from harmful algae — both of which can harm swimmers. The agency posts notices advising against swimming on weeks when levels exceed state standards, but many people do not see or heed the warnings.

Last week’s tests showed 31 of the beaches tested within safe levels for swimming. This includes Backbone, Macbride, near Solon, and Pleasant Creek, near Palo.

At eight state park beaches, swimming is not advised because of high levels of either E. coli or algal toxins. These are:

Iowa DNR weekly advisories are available online or over a hotline at 515-725-3434. Two state park beaches — Lake Geode and Lake Ahquabi — are closed this summer for renovations so the water isn’t being tested there.

A Gazette and Investigate Midwest review of 20 years of beach monitoring data last year showed E. coli has been a constant problem at Iowa beaches. One-fifth of tests administered since 2002 exceeded the state threshold, which is 126 units of bacteria per 100 milliliters of water.

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Backbone, where 86,000 acres of farmland drain into a 50-acre lake, often has had more weeks with E. coli warnings than without in those two decades. Last year’s investigation showed the annual geometric mean of E. coli levels at the beach at Backbone exceeded the state threshold in 14 of the last 20 years.

The E. coli at Iowa beaches likely comes from feces from wildlife and manure runoff from farm fields. These bacteria levels often spike after a heavy rain. Accidentally ingesting contaminated water can cause diarrhea, cramps, nausea, headaches or other symptoms, the Mayo Clinic reported.

The lake at Terry Trueblood Park in Iowa City, while not at one of Iowa’s state parks, remains is closed to swimming because of E. coli.

Occasions when algal toxins exceed safe standards at Iowa beaches have risen and fallen since 2006, The Gazette review showed. Toxins often climb with drought, as the algal blooms thrive in warm, stagnant water rich with phosphorus and nitrate.

Drinking microcystins from algae can cause cramps, headache, vomiting, nausea, diarrhea and pneumonia, the U.S. Environmental Protection Agency reported.

Comments: (319) 339-3157; erin.jordan@thegazette.com