There's a pretty good chance that people who went swimming in a lake over the weekend came away with a skin infection called "Swimmer's Itch".
Doctor Dennis Perry at McLaren Greater Lansing Primary Care says the condition is annoying but not dangerous.
Parasites in the water burrow into the skin and cause a rash of red pimples or blisters. The parasites die pretty quickly but the rash can stick around for a week.
The best treatments are antihistamines and anti-itch creams. You should see a doctor immediately if you see pus or other signs of infection near the rash sites.
Birds and snails carry the parasites, so it's best not to go swimming in areas where you see a lot of them. The parasites tend to concentrate in shallow, rocky areas, which is why kids tend to get swimmer's itch more often than adults.