The downpours sent sewage-fouled runoff out of Baja California and into the surf off the coastlines of Tijuana Slough National Wildlife Refuge and Border Field State Park, and possibly as far north as Imperial Beach and the Silver Strand in Coronado, according to the county Department of Environmental Health.
Signs warning of contamination hazards will stand in all the potentially affected areas until follow-up testing determines that they are safe for recreational use.
County officials also issued a general advisory stating that coastal waters -- including Mission Bay and San Diego Bay -- should be avoided for 72 hours after rain.
Bacteria levels can rise significantly after rainfall, especially near storm drains, creeks, rivers and lagoon outlets that discharge urban runoff. The runoff may contain bacteria from a variety of sources including animal waste, soil and decomposing vegetation.
The heightened bacteria levels may stick around depending on the intensity of the storm, the volume of runoff and ocean conditions, according to the county.