Some of California's most famous beaches - including one in celebrity playground Santa Monica - are hiding disgusting secret

Several iconic California beaches are among the dirtiest along the West Coast thanks to sewage runoff and pollution, a new report found. 

Ten beaches along the shores of California and Baja California, including around the Santa Monica Pier, received the poorest water quality ratings in Heal the Bay's annual report card released on Wednesday. 

The ratings are based on water samples tested for fecal pollution taken last year during dry periods between April and October. 

Many of the shorelines had heavy levels of bacteria due to rainfall that overwhelmed sewage systems and washed pollution into the ocean.

'One of the things that contributes to the poor water quality that we see in a lot of Southern California is how urbanized our communities are,' Heal the Bay Chief Executive and President Tracy Quinn told The Los Angeles Times.

Beaches along the shores of California and Baja California, including around the Santa Monica Pier (pictures), received the poorest water quality ratings on the West Coast

Linda Mar Beach (pictured) is hit with pollution through San Pedro Creek, which channels urban runoff directly to it

'Nearly every square inch is covered with buildings or concrete or asphalt, and that means we have more storm water collecting more pollution and heading for coastal waterways.'  

Approximately 38 million gallons of sewage spilled into the ocean and coastal waterways due to increased rainfall this year, the report found.

Coastal counties in California received 31 percent more rainfall than the 10-year average.

Tijuana River Mouth ranked the filthiest due to persistent sewage issues. Over 100 billion gallons of raw sewage from Mexico's Tijuana River, dumped into the Pacific Ocean over the past five years, originating from inadequate sewage infrastructure.

A significant portion of the raw sewage originates in impoverished Tijuana colonias, neighborhoods where residents lack proper housing due to poverty, according to Fay Crevoshay, the communications and policy director of the international nonprofit WILDCOAST. 

Imperial Beach, once a renowned surfing destination, has fallen victim to the the wastewater surges that have been washing ashore for decades and has been dubbed the 'stinkiest beach in America.'

Playa Beach, Tijuana Slough, Border Field State Park and El Faro all made the list due to sewage exposure from the Tijuana River.

In Santa Monica - a celebrity playground home to A-listers such as Matt Damon, Bradley Cooper and Adam Levine - the iconic pier is plagued with bird feces and urban runoff that contributes to its poor water quality.

Linda Mar Beach, located in affluent Pacifica, is hit with pollution through San Pedro Creek, which channels urban runoff directly to it.

The median property value in Pacifica was $1.19 million in 2022, according to the U.S. Census Bureau.  

Tijuana Slough (pictured) - and other beaches along the Tijuana River - suffer from persistent sewage issues due to inadequate infrastructure 

Border Field State Park (pictured) is affected by heavy sewage pollution from the Tijuana River

Lakeshore Park faces pollution problems due to its location within a network of stagnant water channels in San Francisco Bay, accord to the report.

Mother’s Beach is stuck in a doom loop of pollution do to its enclosed geography within Marina Del Rey - where Ice Cube lives in a $7.25 million mansion - which limits wave action and water circulation. 

Chemicals, trash and fecal matter pose threats to both human health and marine ecosystems. 

Experts recommend to avoid going into waters 72 hours after it rains in California, to pay attention to pollution advisories, and to rinse off after swimming.