SANTA MONICA—The Santa Monica Pier, located in Los Angeles County, is one of the most polluted beaches in California, according to environmental advocacy group Heal the Bay.

The Annual Beach Report Card was released on June 9 and Heal the Bay listed the top 10 most polluted beaches in Southern California. Santa Monica Pier was listed as the sixth most polluted beach.

Heal the Bay analysts assigned A-to-F letter grades to many California beaches based on the levels of weekly bacterial pollution, which can cause gastrointestinal illnesses. Ninety-six percent of beaches received A or B grades during April through October 2016.

During the wet winter, Heal the Bay gave nearly half of LA County’s beaches F grades because the rain created billions of gallons of polluted runoff, which poured into storm drains and out to the ocean. Higher grades indicate lower risks of getting sick after being in the water.

Heal the Bay is advocating for better infrastructure to capture and reuse storm water rather than allowing it to “flow uselessly to the sea.”

Construction is set to begin in Santa Monica on an underground storage tank that will hold up to 1.6 million gallons of captured storm water, which will be transferred to a water recycling facility. According to Heal the Bay, the new storage tank will improve water quality at the pier by reducing the amount of storm water entering the Santa Monica Bay.