For the second time in a week, the threat of bacteria that can sicken swimmers has arisen on popular Twin Cities lakes.
Beaches on Lakes Minnetonka and Calhoun were among several closed Wednesday after tests revealed unsafe levels of E. coli bacteria, which can cause diarrhea, abdominal cramps or, occasionally, more serious problems.
Last week, the state Health Department announced that three swimmers contracted E. coli near Big Island in Lake Minnetonka, leaving one swimmer hospitalized.
The bacteria are the most common reason beaches are closed in the summer, but they are serious enough for officials to post the "No Swimming" signs on the beaches and urge people to stay away.
"We test on a regular basis," said Brett Altergott, parks and recreation director in Lakeville, where Valley Lake Beach has been closed since last Thursday. "This is all done in public safety."
E. coli in lakes often comes from runoff after a rainfall, where animal feces are caught up in the stormwater and swept into lakes before the water can be treated. Sometimes an undiapered child is the culprit.
Officials are not sure what has caused the recent spate of beach closings due to E. coli. Other theories range from high water temperatures that could help the bacteria live to an increase in sightings of birds, which sometimes can be carriers of infectious diseases.
"So many factors play into what cause these kinds of things to happen," said Hennepin County Public Health spokesman Bill Belknap, whose department monitors Excelsior Beach. "It's hard to predict."