Beach & Creek Monitoring Program

San Mateo County routinely tests 43 sites each week, including ocean beaches, creek mouths (where the creek meets or crosses the beach) and Bay/lagoon beaches. Sites are sampled every Monday morning by a combination of County staff and volunteers, primarily associated with the local chapter of the Surfrider Foundation. The County evaluates the potential presence of disease-causing organisms by testing for “indicator” bacteria. When high indicator bacteria levels are found, the site is posted with a warning sign and is re-tested to confirm the results.

Samples are analyzed by the San Mateo County Public Health Laboratory for three bacteria indicator parameters specified by State regulations. These indicator bacteria include total Coliform, Escherichia coli (E. coli) and Enterococcus. Sample analytical results for these indicator bacteria are evaluated against both a single-sample maximum and against the geometric mean of at least five weekly samples (collected within a 30 day period) for each parameter. The State-specified trigger levels for each parameter are, for the single-sample maximum and geometric mean respectively, total Coliform (10,000 or 1,000), E. coli (400 or 200), and Enterococcus (104 or 35), all in units of most-probable-number of colony-forming-units per 100 milliliters (mpn/100ml).

If a site exceeds state standards, the site is posted with Water Quality Advisory/Warning signs. Advisory or Warning signs have red and black lettering on a white background and state: “These waters are contaminated and are not suitable for swimming or other water contact activities.” Warning signs are posted when bacterial standards have exceeded state swimming standards but there is no confirmed source of contamination.

Persons using recreational water posted by County Health Officials do so at their own risk. These signs are posted to alert the public that there may be a risk of illness associated with swimming in contaminated waters and are an advisory rather than a quarantine or beach closure.

When there is a confirmed sewage spill that directly affects a beach, the beach is posted as CLOSED. The beach is not re-opened until it has been tested for indicator bacteria as described above and meets minimum standards for human contact.

Avoid waters which are posted with warning signs or which look unhealthy. Obvious signs of unhealthy water include stagnant, frothy black or brown water, or cloudy white or off-white colored water, or water with an offensive odor. An oily slick or sheen may indicate gasoline or oil products in the water.

When swimming at ocean beaches with creeks that cross the beach, it is best practice to avoid recreational activity in the creek, as well as in the ocean water in the immediate area where the creek meets the ocean. While the creek water may look calmer and safer for you or your child to play in, it typically has higher bacteria counts than the ocean water.

Avoid going in the water during rainstorms. Swimming in areas close to urban streams and storm drain outlets should be avoided during and for up to three days after the end of a rainfall event due to the increased levels of bacteria caused by rainfall runoff.

Swimming in water that is contaminated by sewage, animal waste, chemicals, or other types of contamination can result in minor illnesses such as skin rashes, eye and ear infections, upset stomachs or more severe and potentially life-threatening diseases such as cholera, hepatitis and meningitis.

Sources of contamination include sewage and industrial waste discharges and contributions from residential sources such as storm drain runoff and domestic animal wastes. Sewage can come from failing septic systems, discharges to storm drains or cracked or blocked sewer lines in sewered areas. Large concentrations of birds or marine mammals may also be sources of contamination, which can result in illness.

In spite of the heavy recreational water use in San Mateo County, there have been very few reports of illnesses linked to water contact. Waterborne illnesses, such as cholera and meningitis, which have life-threatening impacts in other countries, have not been shown to be a problem at local swimming areas.

Typical symptoms of the illness, caused by the presence of disease-causing organisms, include skin rashes, ear and eye infections, gastrointestinal upsets (such as diarrhea, nausea and stomachaches), open wound infections and persistent headaches.

See your doctor based on the symptoms you experience. If you think your illness was due to water contact within San Mateo County, please contact County Environmental Health Services at 650-372-6200 to make a report. The information you should provide is: name, dates and areas where you were swimming, symptoms, reasons you believe you got sick from swimming and a telephone number that you or your health care provider can be reached for any other information we may need.