Heal the Bay, a nonprofit environmental group, found the Long Beach shoreline to have the most polluted beaches in the state. In their annual study, they graded more than 500 beaches based on levels of bacterial pollution.
Overall, most California beaches showed good-to-excellent water quality in the survey but seven of the ten most polluted sites were spotted in Los Angeles County. The researchers still don’t know the cause of increased pollution levels and report it is a mystery that requires prompt solution.
One of the reasons of LA county being the most polluted could be due to the fact that they are the ones who first began collecting samples in front of flowing storm drains and creeks. Monitoring closer to pollution sources is a better way to ensure public health.

Most bacterial contamination occurs during winter, when heavy rains overload storm drains and sewage systems and wash waste into the sea. Swimming in such polluted water can cause gastrointestinal, respiratory and other illnesses.

Long Beach, having the most polluted beaches, dragged down the county's results.

Pollution in Santa Monica Bay is not a new problem. It has been present for years. Some of the area's most famous beaches have repeatedly received poor grades from Heal the Bay.

The 10 most polluted beaches ranked by the Heal the Bay are all of Long Beach, Castlerock Beach in Los Angeles County, Marie Canyon storm drain in Malibu, Avalon Beach on Catalina Island, Surfrider Beach in Malibu, the Santa Monica Municipal Pier, Campbell Cove State Park Beach in Sonoma County, Venice State Beach in San Mateo County, Arroyo Burro Beach in Santa Barbara and Cabrillo Beach in Los Angeles County.
While Southern California did poorly, Central and Northern California did pretty well on the report card. Humboldt and San Francisco as well as Marin, San Mateo, Santa Cruz and San Luis Obispo counties received excellent grades at every sampling location.