The public is advised not to use Keller Beach at Miller/Knox Regional Shoreline in Richmond following reports of "swimmer's itch" and tests showing unsafe bacteria levels.
"Swimmer's itch, also called cercarial dermatitis, appears as a skin rash caused by an allergic reaction to certain microscopic parasites that infect some birds and mammals," according to the Centers for Disease Control and Prevention. "These parasites are released from infected snails into fresh and salt water (such as lakes, ponds, and oceans)."
Contra Costa County Environmental Health officials have issued an advisory and signage will be posted.
There are no serious health effects from swimmer's itch, but it is a nuisance for those afflicted, according to county officials.