The Minnesota Health Department reports at least 72 people fell ill as a result of parasitic and bacterial contamination in a Zumbrota campground's swimming areas.
The illnesses involved the parasite cryptosporidium and a potentially fatal strain of E. coli bacteria, said epidemiologist Trisha Robinson. Both can cause diarrhea and vomiting for at least three days and can require hospitalization.
"We know that there are people who have been sick, and while they were sick they went in the water. You know it's likely that people are re-introducing the contamination into the water," Robinson said. "That's why it's so important that people, no matter where they are, not go swimming while they're sick."
Health officials say people became ill from July 1 to August 3.
The campground has re-opened the pool after hyper-chlorinating the water, closed a waterpark that couldn't be treated and posted warning signs about not swimming with diarrhea.
"These are very potentially severe infections," Robinson said. "So it's not like a 24-hour bug. On average these people have been sick for 6 days. And so they're very real illnesses."