Beach bacteria a concern after rain in San Mateo County

After heavy rainfall, many of the county’s beaches post warning signs cautioning beachgoers to not go in the water because bacteria levels exceed health standards. 

For many, the thought of heavy rainfall is good news but what may be an overlooked issue, such as runoff that washes pollutants and bacteria through our local creeks that eventually lead out to many of San Mateo County’s beaches.

Ryan Searcy, executive committee member of Surfrider Foundation, has worked for the foundation for 10 years. His focus, beach water quality, started about five years ago when he worked for Heal the Bay. Heal the Bay puts out an annual beach report card on beaches in California based on their water quality.

“Which has ranked some of San Mateo County’s beaches pretty poorly over the last 10 years,” Searcy said.

On Monday, Dec. 20, San Mateo County beaches were sampled for bacteria and the result left eight beaches, including Linda Mar, Dunes and Venice beaches with warning signs. Furthermore, Bay beaches and creeks were not sampled but maintained warning signs from previous testing results that indicated high bacteria levels. Some notable beaches on the list were San Mateo’s Aquatic Park and Marlin Park in Foster City.

According to the San Mateo County Health website, beaches here are generally safe to swim in but as a precaution to ensure the public’s safety, health officials sample the beaches regularly and report results to the public.

Surfrider Foundation focuses on ensuring beaches are safe, clean and accessible. Searcy added that some of Surfrider’s best efforts are under the Blue Water Task Force. A program within the foundation, composed of volunteers who sample local beaches for Fecal Indicator Bacteria, or FIB, and then report the bacteria level results.

“And that information enables people to weigh risks for themselves, but also, it gives us data to use in our advocacy work, to say hey, like this beach is exceeding the legal limits,” Searcy said.

According to Swimguide.org, San Gregorio Creek met water quality standards 50% of the time in 2021. The creek failed in October of 2021, the same month that San Mateo County experienced heavy rainfall from an atmospheric river.

And that’s not the only waterway in San Mateo County that struggles with water quality. According to the San Mateo Conservation District website, San Pedro Creek and Pacifica State Beach are listed as impaired water bodies on the Clean Water Act 303(d), for fecal contamination from humans, horses, wildlife and dogs.

Searcy said that the risks of swimming in water with high levels of FIB include acute ailments, such as skin rash, ear infections, stomach flu and could contribute to death.

According to the San Mateo Conservation District website, dog waste produces more bacteria in one day than a person, horse and cow combined. The rain flushes the bacteria and organisms in dog waste to nearby waterways that can contaminate the water, affecting sea life and people who swim or surf in the connecting beaches.

The website suggests picking up after pet waste at home and on walks, using specially-designed compost bins for horse manure, and limiting the use of pesticides on lawns and gardens.

Reid Bogert, specialist of the San Mateo Countywide Water Pollution Prevention Program believes dog waste isn’t the only culprit. Bogert said that nitrogen from nearby farms and agricultural work could contribute to the high FIB levels in rain runoff.

Searcy added that there are numerous ways that heavy rainfall contributes to an increased pollutant load in the runoff.

“Runoff is collecting contamination as it is flowing through impermeable surfaces. So rain doesn’t seep into the ground if there’s asphalt or concrete around,” Searcy said. “And so it’s just picking up whatever’s been sort of sitting on those things.”

Visit smchealth.org//beaches for more information.

Note to readers: This story has been changed because it said Marlin Park was in Redwood Shores. While there is a Marlin Park in Redwood Shores, it was not the correct park.