State health officials have confirmed three E. coli O157:H7 illnesses linked to swimming in Lake Minnetonka -- the state's first waterborne outbreak of the summer.
The illnesses occurred in young adults who reported swimming and boating in the Big Island area of the lake on July 4. One person was hospitalized and has since recovered.
All public beaches on Lake Minnetonka remain open and have passed their regular water quality monitoring tests, the department added.
The source of the outbreak is unknown. Lakes can be contaminated by animal waste, septic systems or sewage spills, improper boat waste disposal or ill swimmers, the department said.
Symptoms of E. coli illness include stomach cramps and diarrhea. Most people recover in five to 10 days. However, the infection sometimes leads to kidney failure and death.
Minnesota Department of Health epidemiologist Trisha Robinson said the best way to prevent water illness is by keeping germs out of the water in the first place. Contamination of any size can cause problems in the water.
"It doesn't mean that people have to have an accident in the water when they're swimming, just the small amount of fecal material on anybody's bottom if they're sick with germs, it can wash off into the water and it can make other people ill," she said. "If swimmers can follow some basic precautions, hopefully we can prevent more outbreaks at other swimming locations."
The Health Department says swimmers should follow these guidelines:
• Don't swim when you have diarrhea.
• Don't swallow lake water.
• Practice good hygiene. Shower with soap before swimming.
• Wash your hands thoroughly after using the toilet or changing diapers.
• Take children on bathroom breaks or change diapers often.
• Change diapers in a bathroom, not at beachside.