SAN DIEGO — San Diego County residents were urged to avoid swimming in the ocean due to potentially hazardous runoff from the storm.

The San Diego County Department of Environmental Health issued an advisory declaring all the "coastal waters of San Diego County" a health hazard to swimmers for at least the next 72 hours.

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"Swimmers, surfers and other ocean users are warned that levels of bacteria can rise significantly in ocean waters, especially near storm drains, creeks, rivers and lagoon outlets that discharge urban runoff," county officials said. "Activities such as swimming, surfing and diving should be avoided for 72 hours following rain."

Heavy rains can cause untreated pollutants from roads and businesses to enter coastal waters, along with untreated human waste from encampments on waterways like the San Diego River, official said.

The ocean is particularly toxic in the South Bay region, where untreated sewage from the Tijuana River frequently flows into the ocean. Tijuana River sewage overflows often force county officials to close public beaches in the Tijuana Slough National Wildlife Refuge, Imperial Beach, Silver Strand State Park, and Coronado.

Tijuana Slough's and Imperial Beach's beaches have been closed for that reason since Nov. 21.