One County In California Has 4 Of The Most Polluted Beaches In The State

Travelers heading to California often build their trip around beach days, with the state's coastline being home to some of the most iconic beaches in the world. All along the West Coast, the beaches offer impeccable views and surf-ready water, from the more rugged cliffside alcoves in the north to the golden sands and piers in the south. Unfortunately, travelers will have to be discerning about where they lay down their towel and dip in the water, since some of California's beaches have gotten heavily polluted. In its 2024-2025 Beach Report Card, the environmental nonprofit Heal the Bay found that four of the most polluted beaches in the state are in San Diego County — the most that any single county accounts for.

Heal the Bay analyzes 500 California beaches annually based on levels of fecal-indicator bacteria in the water and gives each beach a letter grade from A to F, with F grades being the worst. Out of the top 10 most polluted beaches based on these indicators, four landed in San Diego County, all receiving F grades: Tijuana River Mouth (ranked third), Tijuana Slough (ranked seventh), Border Field State Park (ranked eighth), and Imperial Beach (ranked ninth). These beaches have had recurring health concerns (for example, Imperial Beach has been ranked one of the filthiest beaches in America), and they're all connected by one driving factor responsible for the pollution: the Tijuana River Estuary.

Crucially, the four beaches that made Heal the Bay's most-polluted list all sit within the same vicinity, along the Tijuana River Mouth close to the U.S.-Mexico border. When the South Bay International Wastewater Treatment Plant was built in Tijuana, Mexico, in the early 1990s, it was intended to treat sewage and discharge it into the Pacific Ocean. Since then, though, Tijuana has grown rapidly and the plant hasn't been able to keep up. According to the San Diego Coastkeeper, the plant discharges around 40 million gallons of raw sewage per day, which flows into the Tijuana River, ending up polluting the area around the river mouth in San Diego. Compounding that is a second source of unfiltered sewage water: the Punta Bandera treatment plant, which has been discharging wastewater out of a concrete pipe that then flows up to the Southern California coast.

The issue has been dubbed the "Tijuana River sewage crisis," and governments on both sides of the border are working on averting the ongoing health threat. In July 2025, the U.S. and Mexico agreed to a deal that promises to repair wastewater pipes, expand the South Bay International Wastewater Treatment Plant's capacity, and divert sewage away from the Tijuana River. The project isn't expected to be completed until the end of 2027, though. For now, the four beaches around the river mouth remain closed, though you can check their updated status at the County of San Diego's Beach and Bay Program site. Despite its challenges, San Diego has plenty of wonderful beaches that are hardly polluted — 12 of its beaches received A+ grades from Heal the Bay, including the pristine Cardiff State Beach, which has perfect surfing and paddling conditions.