San Gregorio State Beach: San Gregorio Creek
Tested by San Mateo County, usually every 7 days.
Taken 25 days ago. Results can take 1 to 3 weeks to be published, and many sites are tested less often in winter.
Every bacteria in this test: Total coliform 2,310 · E. coli 226. The grade follows the worst one against its own limit.
Grade D over 5 tests from Sep 21, 2026 to Oct 19, 2026. 4 were over the limit.
The latest test passed
Stay out for 72 hours after any rain of 0.2 in or more, when runoff raises bacteria everywhere along the coast.
Total coliform over time
No National Weather Service rain gauge is within 20 miles of this site.
- Monday, Oct 19, 2026Total coliform 2,310 · E. coli 226
- Tuesday, Oct 13, 2026Total coliform 24,196 · E. coli 197
- Monday, Oct 5, 2026Total coliform 19,863 · E. coli 41
- Monday, Sep 28, 2026Total coliform 11,199 · E. coli 189
- Monday, Sep 21, 2026Total coliform over 24,196 · E. coli 85
- Monday, Aug 17, 2026Total coliform over 24,196 · E. coli 160
- Monday, Aug 3, 2026Total coliform 17,329 · E. coli 187
- Monday, Jul 27, 2026Total coliform 6,488 · E. coli 988
- Monday, Jul 20, 2026Total coliform 1,497 · E. coli 233
- Monday, Jul 13, 2026Total coliform 4,106 · E. coli 588
Enterococcus and coliform bacteria live in the guts of people and animals. Health departments test for them because they travel with sewage, runoff and animal waste, so a high count is a warning that germs that do make people sick are likely in the water too. Clear water can still be contaminated: bacteria and viruses are too small to see.
San Diego County's DNA test (ddPCR) counts bacterial DNA instead of growing the bacteria in a lab, so it returns results the same day. Its numbers run higher than the older lab tests, which is why its safe limit is 1,413 rather than 104. The two are never compared on this page.
San Diego County's health department says swimming in water under an advisory can cause stomach illness, such as diarrhea and vomiting, and skin and ear infections. The EPA's national swimming guidelines are set at a level where about 32 to 36 of every 1,000 swimmers would get a stomach illness. A study of San Diego surfers found about 12 extra stomach-illness cases per 1,000 in wet weather, highest during rain and the day after, and back near normal 3 days later.
The grade is Nautical Nick's, built on the official limits: A is a quarter of the limit or less, B half or less, C under the limit, D over it, and F more than 10 times over. When a county posts an advisory or closes a beach, its sign is the final word.
Sources: California State Water Board beach test results; San Diego County Department of Environmental Health sample reports; Surfrider Foundation Blue Water Task Force; National Weather Service daily rain totals via the Iowa Environmental Mesonet. Limits: California Code of Regulations, Title 17, Section 7958.