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Fewer people partied at Lake Minnetonka’s Big Island over July 4th, but the Hennepin County Sheriff’s Office said it saw an uptick in boating under the influence incidents on the lake.

Traffic to Big Island was down about one-third over the holiday weekend. Six people were ticketed for boating under the influence on the lake, compared with three at the same time last year.

More Water Patrol deputies were assigned to the lake, and the vast majority of stops were educational. They issued nearly three times as many verbal warnings as citations.

There were 198 verbal warnings and 51 citations. Seven people were taken to hospitals.

Overall, it was much calmer than last year when there were five assaults and a large fight on a boat, according to the Sheriff’s Office. Also, several hundred people who tied up boats at Big Island became ill with diarrhea and vomiting.

Health officials weren’t able to identify the exact pathogen that caused the illness, but they did say they believe that the outbreak was the result of something in the lake water, which was ingested by those at the lake.

The outbreak came as high levels of E. coli forced 11 Twin Cities beaches to temporarily close. The number of closures peaked at 49 and 45 in 2015 and 2016, respectively, when summer rainfalls were heavier than average. But unlike most of those cases, caused by rain runoff tainted with animal feces and other contaminants, officials say the Big Island health scare was caused by humans.

Some people speculated that a boat illegally dumped its sewage. Another possibility, health experts said, was that a single person with norovirus defecated or vomited in the water, exposing hundreds to waterborne illnesses.

Big Island is part of a nature center on 56 acres in Orono. The island used to have an amusement park and veterans camp but is now widely known for its Cruiser’s Cove, a popular spot where boats tie up for partying.

David Chanen • 612-673-4465