In July 2013 state health officials in Minnesota identified three cases of E. coli O157 illness in Minnesotans linked to swimming in the Big Island area of Lake Minnetonka. The illnesses occurred in young adults, and all were residents of the seven-county metropolitan area surrounding the lake. All of the cases reported swimming and boating on July 4. One patient was hospitalized. The source of the E. coli in the water was not determined.