Swimmer's itch

Parasites in contaminated water can enter the superficial layers of exposed skin — skin not covered by a swimsuit, wet suit or waders. The organisms soon die and cause a skin reaction called swimmer's itch. Initially, the reaction is mild and consists of redness of the affected skin followed by itchy, red, raised areas. On subsequent exposures to the organisms, the reaction can be more severe and persistent, sometimes causing blisters.

Swimmer's itch isn't serious and usually resolves without medical treatment within one week.