The normally crowded beaches around Bde Maka Ska have missed their typical buzz this summer.
When E. coli was discovered in the lake on July 2, the Minneapolis Park and Recreation Board closed the Thomas and 32nd Street beaches. On July 15, E. coli levels exceeding state guidelines were recorded at North Beach, which was closed for 15 days. The Thomas and 32nd Street beaches remained closed as of press time.
So, what’s causing the elevated E. coli levels?
“It’s hard to say exactly,” said Rachael Crabb, water resources supervisor for the MPRB.
Two likely candidates are high rain levels and birds, she said. The Twin Cities are experiencing an extremely wet summer with major rain storms hitting with increasing frequency, a trend experts expect to continue as the climate warms.
Increased rainfall leads to higher lake levels — Bde Maka Ska, Cedar Lake and Lake of the Isles all have been about 1.5 feet above average this summer — which in turn leads to more shoreline erosion. Wet sand can also contribute to higher E. coli levels, Crabb said.
Bird feces is a common culprit. If waterfowl nest close to beach areas, their droppings can end up in the lakes and contaminate the area, she said. Although temporarily high E. coli levels are not uncommon, having sustained high levels on Bde Maka Ska is.
“This is unusual,” Crabb said.
No illnesses due to E. coli were reported in people visiting the lake, but some permanent residents of the Chain of Lakes have had tough summers. A late-July heat wave, combined with bacteria discovered in local crappie populations, led to a summer fish kill in lakes across the city.
Fish kill is not an uncommon phenomenon in Minnesota lakes and often happens in the early spring as ice melts and on hot days in the summer. Fish kill is the result of oxygen loss, Crabb said. On extremely hot days, water holds less oxygen and some (usually smaller) fish struggle to survive.
Summer fish kills have previously hit Minneapolis lakes, most recently in 2011 and 2004, Crabb said. But this year the fish kill occurred in several water bodies at once, including the entire Chain of Lakes, causing putrid smells around lakeside trails across Southwest as Park Board staff worked to get the carcasses out of the water.
“It was kind of unusual to have so many fish kills in so many lakes,” Crabb said.
Most of the victims were crappies around four inches in length. The Minnesota Department of Natural Resources collected samples of the dead fish and found strains of diseases in the crappie population, Crabb said. Two different bacteria were discovered in the crappies.
While it’s been a tough summer, Minneapolis lakes are fairly healthy. The Minnehaha Creek Watershed District gave Bde Maka Ska and Lake Harriet “A” ratings in 2017, while Cedar Lake and Lake of the Isles received “C” grades.
“We’ve put a lot of investment into the Chain of Lakes and it shows,” Crabb said.