Bacteria in Pine Lake State Park have continued to increase since the state posted a swim warning last week. (Photo courtesy of Iowa Department of Natural Resources)
Swimming is not recommended at the beaches of two state parks after weekly tests recently showed they have potentially unsafe concentrations of bacteria, according to the Iowa Department of Natural Resources.
One of them — at the lower lake of Pine Lake State Park in Hardin County — had about triple the bacteria concentration of last week, when it was also subject to the swim warning.
Those concentrations can change significantly over the course of days. The test at Pine Lake happened Tuesday.
The other beach with a swim warning this week is at Prairie Rose State Park in Shelby County. A test there on Wednesday revealed a bacteria concentration that was six times the state’s safety threshold, and it was slightly higher than Pine Lake’s concentration.
Two beaches that had warnings last week had little or no detectable bacteria this week. Those were at Union Grove State Park in Tama County and Lake Keomah State Park in Mahaska County.
A beach at Lake Darling State Park has had detectable amounts of blue-green algae toxins the past two weeks, but they diminished this week and are less than half of the safety threshold that would trigger a swimming warning.
The DNR gathers data about city and county beaches but does not issue warnings for them. Tests this week revealed potentially unsafe bacteria concentrations at two of them: Bigelow County Park in Woodbury County and Old Water Plant Beach in Storm Lake.
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