IMPERIAL BEACH, Calif. -- Authorities on Saturday banned swimming and surfing from Imperial Beach to the Mexican border because of a likely flush of sewage-contaminated storm runoff from the Tijuana River.

The water contact closure area stretches from the Tijuana Slough National Wildlife Refuge north to Carnation Avenue, on Imperial Beach's north end, according to San Diego County's Department of Environmental Health.

Heavy rainfall has again overwhelmed Tijuana's sewage system, and sewage-laced runoff from the Tijuana River is flowing northwest into the Tijuana Estuary, which is in the United States. Observations today showed ocean currents were moving north, which could move the runoff-contaminated ocean water up to Imperial Beach, health officials said.

Signs warning of sewage contamination have been set up on the beach and will remain in place until field measurements show the ocean is safe for swimmers, according to the environmental health department.