Nearly 120 people have reported getting sick after boating near Big Island on Lake Minnetonka over the long July 4th weekend, Hennepin County Public Health officials said.

As of Wednesday morning, the county said that 116 boaters on Minnetonka reported having been at Big Island during the holiday weekend and have since experienced vomiting and/or multiple episodes of diarrhea.

The Minnesota Department of Health is working to help determine the cause.

Eric Evenson, director of the Lake Minnetonka Association, said that he and a group went out to pick up litter around Big Island on Sunday. "We don't know if it's related or not, but one of the guys who helped got sick later," he said.

Meanwhile, several beaches in the metro area remain closed after authorities found E. coli in the water.

On Tuesday, Hennepin County closed the swimming beach at the Commons Park in Excelsior. It's not far from Big Island, but the beach's bacteria level there isn't necessarily related to the Big Island illnesses, authorities said.

State health officials are working determine the cause of the illnesses reported by people who were boating near Big Island.

Several beaches in Minneapolis and Chaska also are closed because local officials found E. coli in the water.

Beach closings due to high bacteria counts don't happen every summer in the Twin Cities, but they aren't uncommon. The duration of the closings this year is longer than usual, said Robin Smothers, a spokeswoman for the Minneapolis Park and Recreation Board, probably because heavy rains exacerbated the problem by washing polluting materials into the lakes.

Stormwater and waterfowl excrement are the main causes.

"In layman's language? Geese pooping. Unless we catch them in the act, which nobody wants to do, it could be ducks as well," she said.

High water levels in the lakes are another factor, said Deb Pilger, the park board's director of environmental management. "Higher water levels brings in more wet sand, which unfortunately is a good environment for bacteria to grow in," she said.

The Minneapolis Park Board last week closed the Thomas and 32nd Street beaches at Bde Maka Ska/Lake Calhoun, and the Lake Hiawatha Beach. On Wednesday, officials said those beaches would remain closed through at least Monday or until bacteria levels drop.

Chaska city officials on Tuesday closed the Clayhole Swim Beach at Fireman's Park, also after finding E. coli in water tests. The beach will remain closed until further notice.

McCarrons Beach in Roseville closed Wednesday and will be retested on Thursday.

On the bright side, Evenson had good news from the post-holiday Big Island cleanup: less garbage than usual.

"I was kind of pleasantly surprised at how little litter we picked up," Evenson said. "Years past, we filled a 40-yard dumpster without any problem at all. This year, we barely filled 10 bags."