Iowa’s annual swim warnings for bacteria highest since 2010

Abundant rainfall that washed fecal material into Iowa's lakes likely led to the largest amount of swimming advisories for bacteria at state beaches in more than a decade, according to the Iowa Department of Natural Resources lake and beach monitoring coordinator.

"It wasn't the highest on-record year, but it was definitely more than recent years," coordinator Dan Kendall said.

The Iowa DNR samples water weekly near about 40 state beaches between Memorial Day and Labor Day for elevated levels of bacteria and algae toxins, which can cause skin irritations, infections and illness. If those concentrations exceed the department's safety thresholds, the state posts notices at the beaches that swimming is not advised.

This year, about 24 percent of the tests revealed unhealthy bacteria concentrations, Kendall said. That is higher than 2015 and 2016 when the percentages were 22, but it is shy of 2010 that had 26 percent.

In total, the department issued 145 swimming advisories this year over the course of 15 weeks. There were 130 for bacteria, seven for toxins and eight for both, according to Iowa DNR data.

Rainfall often leads to higher bacteria concentrations because the water flushes fecal matter from large birds and other animals into the lakes. This has been the ninth-wettest year statewide in more than 130 years, according to Iowa State University data.

Calm and hot conditions can stoke algae blooms that release the toxins. Fertilizer runoff from crop fields also contributes to the blooms — when algae grow rapidly in one area of a lake. But there were fewer warnings related to toxins this year than last year.

Two dozen different beaches — more than half of those that are monitored by the state — had swim warnings at least once this year.

Where to swim

State beaches nearest to Cedar Rapids are safe for swimming this Labor Day weekend: Backbone State Park near Dundee, Pleasant Creek Recreation Area near Palo and Lake Macbride State Park near Solon.

But the beaches at Coralville Lake have unsafe bacteria concentrations, according to the Army Corps of Engineers, which monitors that water. Geese, seagulls and turkey vultures have been ever-present there recently.

State beaches with swim warnings this weekend include:

Backbone State Park had swim warnings for nine straight weeks for bacteria, but not for the past two.

Beeds Lake State Park had advisories for 13 of the 15 weeks monitored — the most for any state beach.

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