The county Department of Environmental Health issued a runoff advisory Wednesday, warning residents to avoid contact with coastal waters from Seacoast Drive in Imperial Beach to the border due to heavy rainfall.
The advisory comes as rain was falling throughout San Diego County. The National Weather Service office in San Diego said the heaviest rain would occur through Wednesday evening and again on Thursday afternoon.
Most areas of the county west of the deserts are expected to get between 1 and 2 inches of rain, with snow falling above 7,000 feet.
Runoff from the Pacific storm will lead to heightened amounts of bacteria in coastal waters. County officials advised residents to avoid water contact for 72 hours after the rainfall ends.
The shoreline of Tijuana Slough National Wildlife Refuge and Border Field State Park will also remain closed due to Tijuana River flows contaminated with sewage entering U.S. waters.