ZUMBROTA, Minn. (WCCO) — A warning tonight for families planning a camping trip in the final weeks of summer.

The Minnesota Department of Health is investigating a waterborne illness that has made at least 72 people sick at a campground since July.

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The outbreak is happening in Zumbrota, about 20 miles north of Rochester.

Health department officials are trying to determine why so many people have gotten sick from a parasite that appears to have contaminated the water at a pool and pond at Shades of Sherwood campground.

Linda Baier and her husband have been living here for 28 years.

“It worries us because we like this place so well and we’ve been here so long,” Linda said. “I personally don’t know of anybody that has gotten sick yet because we’re down in all three parts of the water and we’ve never gotten sick.”

The health department is looking into whether the water in the swimming pool — as well as a man-made pond and the Zumbro River — is exposing people at this campground to the parasite Cryptosporidium.

The most common symptoms are diarrhea and vomiting. The first case was reported on July 1, and the number of illnesses has continued to climb.

Mike Thoreson is the owner of Shades of Sherwood campground.

“The number that they’re putting out there of 72 people have not been confirmed cases. These are just people that they’ve talked to on the phone that have said they’ve been sick and also stayed at Shades of Sherwood campground,” Thoreson said.

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Thoreson says the information released by the health department is hurting business.

“Since these releases that they keep putting out, we’ve seen our numbers cut in half for every one of these weekends moving forward,” he said.

Linda Baier says she hopes everything is sorted out soon.

“This is a lovely place, it’s a fantastic place,” she said. “I don’t know what we’d do if something happened. We have nowhere else to go.”

The owner of the campground said he is working with the health department to prevent more illnesses.

No new cases have been reported since Aug. 3.

The swimming pool was temporarily closed and hyper-chlorinated to kill any existing parasites, but it is now open.

The man-made pond remains closed because the health department says it was constructed in such a way that it cannot be effectively treated to remove the parasite.

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For more information, visit the Minnesota Department of Health website.