The county health department has extended a shoreline closure to include Imperial Beach amid concerns of sewage-contaminated runoff, the agency said.
The water contact closure initially issued on Nov. 29 was expanded on Wednesday to include the shoreline from the U.S.-Mexico border to the north end of Imperial Beach.
The county Department of Environmental Health said people should avoid going into the water until testing has deemed it is safe for recreational use. Signs will be posted to notify beachgoers of the closures.
San Diego's first significant storm of the fall season initially prompted the recent water contact closure, though closures are common during the rainy fall and winter months.
Sewage-contaminated waters can flow into the United States when a diverter, part of an agreement between the U.S. and Mexico, is shut down during heavy rainfall, according to the DEH.
Contaminated waters can then flow northwest via the Tijuana River, which crosses the border just west of the Otay Mesa Port of Entry, through the Tijuana River Estuary and into the Pacific Ocean south of Imperial Beach.
The constant closures and contaminated flow from Tijuana has long sparked contention between the South Bay community and the International Boundary Water Commission (IBWC), the agency that manages issues that affect both the U.S. and Mexico's waters.
In September, the San Diego Water Board sued the U.S. section of the IBWC, claiming it is violating the Clean Water Act by not monitoring or stopping untreated waste flowing to the ocean.
Several San Diego municipalities have also teamed up to file a federal lawsuit against the agency.
The IBWC said they have not violated any environmental laws and have actually "reduced the problem's scale" with the construction of a San Diego treatment plant.