Officials are warning residents about swimmer's itch after cases were reported on East Okoboji Lake in the Iowa Great Lakes Region.
The state Department of Natural Resources says people should avoid swimming in marshy areas and places containing aquatic plants.
Swimmer's itch is caused by a parasite, but officials say most cases do not require medical attention. They can be treated with anti-itch lotions and other creams used for most skin allergies or irritations.
Officials recommend that people limit the time they spend in water and towel off quickly afterward. That helps remove parasites from the skin's surface.
Welts and itching caused by parasites can last for several days to about a week.