County officials issued a water contact closure Sunday for the shoreline at at the border due to water samples exceeding state health standards.
The San Diego County Department of Environmental Health and Quality said the closure includes all beaches from the international border to the south end of Seacoast Drive. The closure includes Tijuana Slough National Wildlife Refuge and Border Field State Park.
Closure signs will remain in place until results meet state health standards for recreational use.
The Tijuana River enters the county from Mexico, flowing through its southernmost reaches before it empties into the Pacific Ocean.
Sewage-contaminated runoff that enters the river in Mexico may be moving north along the San Diego County shoreline, according to a statement in June from the health agency.
Beaches in southern San Diego County have been closed off and on all year.
On July 17, officials lifted a water contact closure after testing showed the ocean was safe for recreational use. Another water contact closure was issued July 25.