VENTURA, Iowa (AP) — A swimming advisory has been issued for McIntosh Woods State Park in north-central Iowa due to E. coli contamination. The Mason City Globe Gazette reports that a sample taken at the lake near Ventura in Cerro Gordo County exceeded a safe amount of the bacteria found in fecal matter.

The Iowa Department of Natural Resources says for that reason, swimming is not recommended at the lake. The department says surface runoff after a heavy rainfall could be the culprit. Sunlight destroys the bacteria and improves the water quality.

The swimming advisory is among five issued throughout Iowa after this week’s sampling. Others include beaches at Prairie Rose, Lake Darling, Backbone and Green Valley state parks.