IMPERIAL BEACH, Calif.—San Diego County health officials have expanded a water closure near the U.S.-Mexico border.

The county Department of Environmental Health expanded the closure Saturday from the Tijuana Slough National Wildlife Refuge north along the shoreline of Imperial Beach.

U-T San Diego ( http://bit.ly/1bl0pz7) reports that health officials believe sewage-contaminated runoff from the Tijuana River entered the Tijuana Estuary due to recent rainfall. Ocean currents may have pushed contaminated water northward to Imperial Beach.

Warning signs to stay out of the water will be posted until measurements show it's safe for recreational use.

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Information from: U-T San Diego, http://www.utsandiego.com