At least 20 people got E. coli infections after swimming in Lake Anna, Virginia lake, with nine hospitalized, says the Virginia Department of Health.

The Virginia lake infections, mostly in children, happened between May 27 and June 4, around Memorial Day weekend.

Officials are testing the lake water to find the source of the contamination, with results pending.

The health department found multiple exposure points around the lake.

Five children with E. coli have developed a severe complication affecting the kidneys.

Swimmers are urged not to drink untreated water or swim with open wounds.

Lake Anna, a popular spot, was created in the 1970s to cool a nearby nuclear power plant

The lake has a "cold" side and a "warm" side, heated by the plant's discharge water.

Ten more suspected cases of E. coli are still being investigated.

Symptoms of E. coli include stomach cramps, diarrhea, vomiting, and fever, which can lead to serious health problems.