There were 25 state beaches this summer where swimming was not advised for at least a week due to high levels of bacteria or toxins or both, according to the Iowa Environmental Council.
The Iowa Department of Natural Resources samples water at beaches weekly from late May through early September, when people are most likely to come in contact with the water. The department tests for levels of E. coli bacteria and blue-green algae toxins, which can cause skin irritations, illnesses and infections.
The 25 beaches with swimming advisories this year represent about two-thirds of the total state park beaches and were a comparable number to last summer, when 24 beaches had advisories.
The IEC has been monitoring the state’s testing program for nearly 20 years but has been unable to identify a definitive trend in bacteria and toxin levels, said Alicia Vasto, program director for the group water.
“Overall, what we understand is that we constantly have beach advisories in the state,” she said. “We constantly see E. coli contamination.”
The toxins are produced by cyanobacteria that can proliferate — or “bloom” — when lake water is warm and calm and rich in nutrients, often from agricultural fertilizer runoff. The flowers turn blue as the food dwindles and the bacteria perish.
This summer, there were 12 weekly advisories for toxins, according to IEC data. That was about half of last year’s number.
But this summer, there were 107 advisories for elevated levels of E. coli, a 22% increase over last year.
Peaks in the bacteria’s presence often follow precipitation that washes into lakes, perhaps from the droppings of geese and cattle, for example. E. coli bacteria also feed on the remains of cyanobacterial blooms.
The water at Lake Darling in southeast Iowa had the most consistently high levels of bacteria this year, the IEC reported. There has only been one week that Darling did not have a bathing advisory in effect. The lake had a total of 14 E. coli and two for toxins.
Bacteria levels can change dramatically from day to day. An example: The concentrations of E. coli at Crandall’s Beach in Spirit Lake were so high in August that they were immeasurable by DNR tests, which can detect up to 24,000 viable bacteria per 100 milliliters of water – or less than half a cup of water. water .
This concentration is more than 100 times higher than the amount that can trigger swimming warnings. But the week after that test, the beach water test showed only 52 bacteria per 100 milliliters, which was below the safety threshold of 235.
The DNR has worked to limit watershed pollution — including bacteria, nutrients from agricultural fertilizers and manure, and eroded soil — from reaching the state’s lakes, but Vasto said more needs to be done. be done.
“It’s really concerning because we have so few public places in our state – we have so little public land,” she said. “And so the public beaches and parks that we have, we really need to protect them and do more to address this issue.”
In a December snapshot of major lake restoration projects, MNR said it had completed 29 projects, 21 were underway and 14 were planned.
Sometimes projects do not solve water quality problems. A $12 million restoration of Lake Darling was completed in 2014, but it often has high levels of bacteria.