After the party, you find out who your real friends are.

You host the dinner party; they load the dishwasher. You spend July 4th partying on Lake Minnetonka; they wade into the water afterward to collect the bottles and beer cans and underpants you dumped around Big Island.

If only that was all you dumped.

We’ve had more than 170 confirmed cases of illness among the people who boated and floated near Big Island over the holiday weekend. The only thing worse than the vomiting and diarrhea and dehydration was the likely source.

“Don’t use the lake as a toilet,” Hennepin County epidemiologist Dave Johnson advised the public Friday.

Sound advice that someone anchored on the lake may not have heeded during a long day of drinking and eating and marinating in warm, crowded waters.

But if people are the cause of most of life’s troubles, we’re also the solution.

Minnetonka’s cleanup crews went into the water the Monday after the big party.

Again and again, they dove under the water, surfacing with lost Ray Bans and Apple watches and party beads. They cleared the shoreline of beer cans and the lake bottom of smashed bottles of Jägermeister.

“It’s really getting a lot better, if you can believe that,” said Gabriel Jabbour, who owns several businesses along the lake and has spent years trying to preserve and protect the waterway.

Jabbour counted at least 30 or 40 volunteers on the cleanup crews that came out Monday morning to clean up a mess they didn’t make.

“These are people who grew up on the lake and who care about the lake,” he said.

The volunteers used to dredge enough garbage out of the lake after Independence Day to fill a 40-yard dumpster. This year, Eric Evenson, director of the Lake Minnetonka Association, estimated the crews hauled out about 10 garbage bags’ worth.

“People are doing a much better job,” said Evenson, who was one of the people cleaning up after the party. “They’re bringing back what they take out.”

Or at least, most of what they take out.

The lake is so crowded during the holiday, people are reluctant to give up a prime viewing spot for the evening fireworks and head back to shore in search of a bathroom — even after their passengers polished off 10 hot dogs and a keg of beer.

The fish might do it, the loons might do it, but that doesn’t mean you get to empty your boat’s toilet into a crowded recreational lake. I don’t care how many hot dogs you just ate.

Don’t put anything in the water you wouldn’t want to swim through.

State and county health officials are still searching for the cause of the outbreak. The victims are resting and hydrating. Excelsior Beach — within eyeshot of Big Island — is closed due to what officials say is an unrelated spike in the E. coli count.

For those still trying to carry out Prince’s advice to purify yourself in the waters of Lake Minnetonka, plenty of beaches remain open and most people are nice enough to stay out of the water if they’ve been sick.

The water, epidemiologist Johnson told reporters on Friday, is “as safe as it usually is” here in the Land of Lakes.

Most Minnesotans will tell you that a day on the lake is worth taking that plunge. Especially when everyone on the water is looking out for each other.

“It’s just common sense,” Evenson said. “You don’t want to mess where you swim.”