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DNR maintains E. coli advisory in 13 Iowa lakes for Labor Day

josquin2000 / Flickr

The Iowa Department of Natural Resources (DNR) has advised against swimming in 13 state lakes over the long Labor Day weekend.

The DNR’s decision is a result of recently collected water samples from throughout the state’s parks. The department has identified a spike in E. coli bacteria that Jason Palmer of the DNR’s Water Quality Division uses as its proverbial canary.

“E. coli is a broad family, with only a few strains that are infectious to humans," he said. "We use it as an indicator for more dangerous threats. Bacteria that’s smaller, in smaller quantities, that’s difficult to test for directly.”

Palmer went on to say that the drought and heat across Iowa in the past week may reduce bacterial lifespan in the state’s water bodies, but not its sources; in fact, they could be amplified by the presence of geese, ducks and even pelicans, particularly toward the end of the summer season as those birds try to keep cool while on their migration paths.

“Those birds use the park and the lake just like humans do,” Palmer said. “During times of drought and heat, it’s likely that those sources are more of a factor in introducing bacteria.”

Another key factor that could contribute to the late summer bacterial spike throughout the state, Palmer said, is agricultural runoff.

The DNR has advised against swimming in the lakes for the past two weeks out of safety for both beachgoers and staff. Water sample collection was put on hold last week due to triple-digit temperatures and resumed just this week.

The Iowa DNR stresses that no cases of E.coli have been reported in humans from interaction with the state’s waters, though the department does encourage safety and awareness of possible risks as vacationers float into Labor Day.

A previous version of this story stated that 11 lakes were under advisory. This number has been corrected to reflect that 13 lakes are under advisory.

Grant Leo Winterer has been Iowa Public Radio’s Waterloo and Cedar Falls reporter and host of Weekend Edition since August of 2023.