These are California’s dirtiest beaches. Where are you swimming this summer?

As Mother Nature continues to turn up the heat this summer, those looking to cool off along the California coast might want to reconsider where they’re swimming. Ten California and Baja California beaches, including around the Santa Monica Pier and a stretch of Mother’s Beach in Marina del Rey, received the poorest water quality grades based on measurements taken last year during dry periods between April and October. Of California’s more than 500 beaches tested last year, 89% received top marks for water quality for the warmer seasons between April and October, when people tend to spend the most time in the ocean. “Nearly every square inch is covered with buildings or concrete or asphalt, and that means we have more stormwater collecting more pollution and heading for coastal waterways.” Heal the Bay’s report included a beach bummer list of the 10 beaches, including two in Mexico, that consistently receive poor marks throughout the year. Some areas in California, including parts of San Diego County, shifted to a new water sampling protocol that doesn’t align with how Heal the Bay calculates water grades, which is why some beaches may not have made this year’s honor roll.