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The temperatures have dipped and the lifeguards have gone home, but the beaches at Lake Nokomis have reopened.

More than three weeks after an E. coli outbreak at the lake sickened at least 73 swimmers, the Minneapolis Park and Recreation Board decided to reopen the beaches Thursday. The date marked three full incubation periods since people were exposed to a strain of E. coli that experts think may have been caused by a sick swimmer.

The swimming season officially ended on Labor Day, meaning there are no longer any lifeguards, docks or buoys at any of the city's beaches. The Park Board is also no longer testing beaches for E. coli.

A record number of beaches closed early this summer, according to Park Board officials. While most shut down because of elevated E. coli levels found during routine testing, Lake Nokomis' beaches were the first in more than 25 years to close because of illness.

Park Board Commissioner Steffanie Musich, who represents the area surrounding Lake Nokomis, believes the city needs to act quickly to prevent similar contamination next season.

"It's not just an issue that is going to impact Minneapolis. It's an issue that will impact the entire state," she said. "People see it in the parks because they're out there and it's visible, but it's impacting private homeowners and property owners, as well."

Greater E. coli levels are mainly caused by rain, stormwater runoff and animal waste, including from geese and other waterfowl. Musich said the city should give homeowners incentives to install green roofs, rain gardens or rain cisterns in order to help manage stormwater runoff.

"To have a bigger strategy around how we help property owners cope with that, I think, would be incredibly important for the city as a whole to be considering," she said.

Minneapolis City Council Member Andrew Johnson agreed, saying the city should spread out its stormwater treatment. The city's 2040 Comprehensive Plan has goals of improving stormwater infrastructure, he said, such as adding "bioswales," or shallow channels on streets that collect and filter runoff.

"The goal is all the same whether it's homeowners [or] public infrastructure," he said. "The more you can have localized storage and treatment, the better. And there's an opportunity for homeowners to be a part of that."

Yet the outbreak in Lake Nokomis wasn't caused by runoff. The strain of Shiga toxin-producing E. coli was not detected by the Park Board's weekly water tests. It was only after three children became sick that the Minnesota Department of Health called for the beaches to close on Aug. 13.

The outbreak would grow to 73 people, all of whom swam at the lake between July 16 and Aug. 11, according to the Park Board. The people who reported being sick mostly suffered from stomach cramps and diarrhea, although some also had a low-grade fever and vomiting, according to the Department of Health. No one was hospitalized.

The Park Board urges people to stay out of the water if they are sick or had diarrhea in the previous week. The should also refrain from swimming one or two days after a rainfall of 0.5 inches or more.

Swimmers should avoid swallowing lake water, and should wash their hands or shower after going in the water. Parents should take their children for regular bathroom breaks and change diapers in changing rooms — not on the beach.

Most importantly, residents across the city should pick up after their pets, as that waste could likely end up washing into the lakes, Musich said.

Miguel Otárola • 612-673-4753