Four San Mateo County beaches made the list of the most-polluted beaches in California, an annual report released Thursday by Heal the Bay, nonprofit environmental advocacy group.
The most-polluted beaches have higher levels of bacteria in the water, according to the group.
The Marina Lagoon in Lakeshore Park in San Mateo County was the state’s second most-polluted beach because of poor water circulation and high bacteria counts.
Linda Mar Beach was right behind Marina Lagoon. Pollution at Linda Mar Beach is due to polluted runoff from San Pedro Creek, according to Heal the Bay officials.
Roosevelt Beach was the fifth most-polluted beach in the state because of nearby storm drain runoff. That’s also the problem at Surfer’s Beach, the 10th most-polluted beach in The Golden State.
Overall, summer water quality grades for Northern California beaches slumped 3 percent this year compared to a five-year summer average.
According to the report, Northern California beaches are those in Santa Cruz, San Mateo, Alameda, San Francisco, Contra Costa, Marin, Sonoma, Mendocino, Humboldt and Del Norte counties.
But Heal the Bay officials also reported 88 percent of the 96 Northern California beaches monitored by the group received grades of A or B. Each beach was assigned a letter grade from A to F.
Swimming at a beach with a grade of C or lower “greatly” increases the risk of getting illnesses such as ear infections, stomach flu, upper respiratory infections and rashes.