E. coli keeps Trippe Lake beach closed
The city is testing the water two to three times each week, but E. coli counts have not yet declined, said Matt Amundson, parks and recreation director. The beach, located on Trippe Lake's northwest side, was closed to swimmers July 20 when tests revealed E. coli exceeded the maximum allowable levels.
The Environmental Protection Agency recommends advisories be posted when tests find 235 colony forming units per 100 milliliter sample. Closures are issued when levels are more than four times that.
Amundson said the latest sample from Trippe Lake Park was about 2,400 CFUs. He said the area typically has counts below 50, but a dry spell last month allowed the bacteria to settle.
Amundson said the beach has a history of closing because of high E. coli readings. Rain forecasts for the coming weekend give him hope the park will take a significant step toward reopening.
"What happens when you have real long hot spells isóbecause how shallow the water isóit just doesn't turn over," Amundson said. "Every body (of water) has levels of E. coli, and when the water is not moving and the geese are out there, (bacteria) just stays there longer."
The city's water department conducts the tests on Trippe Lake, which averages about 4 to 6 feet in depth.
The E. coli itself does not worry biologists, but the E. coli spike increases the probability that other bacteria and viruses are present.
"We use it as an indicator," said Heidi Bunk, regional lakes biologist at the state Department of Natural Resources.
Summer typically leads to an increase in E. coli, partly because warmer weather encourages the growth of bacteria. Fecal matter from waterfowl and runoff are two major causes of E. coli.
Lions Beach in Janesville temporarily closed last month after tests showed levels of E. coli greater than the acceptable amount. Pewaukee Lakefront Beach shut down for two days for the same reason.
Bunk said there are several measures communities can take to protect the water and lower the E. coli threat. That includes installing rain gardens to absorb rainfall and prevent runoff.
Those measures typically are taken on waters that have larger bacteria problems.
Amundson said the lake is still open to fishing. E. coli is mostly a threat to swimmers and those who could ingest the water.