Mad River Beach Co. Park: Clam Beach near Mad River
Tested by Humboldt County, usually every 7 days.
Taken 18 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 20 · E. coli under 10. The grade follows the worst one against its own limit.
Grade A over 4 tests from Sep 30, 2026 to Oct 26, 2026. None 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
- Monday, Oct 26, 2026Total coliform 20 · E. coli under 100.28 in of rain in the 3 days before
- Tuesday, Oct 20, 2026Total coliform 31 · E. coli 10
- Monday, Oct 5, 2026Total coliform 31 · E. coli under 10
- Wednesday, Sep 30, 2026Total coliform 20 · E. coli under 10
- Tuesday, Sep 22, 2026E. coli under 10
- Tuesday, Sep 8, 2026Total coliform under 10 · E. coli under 10
- Monday, Aug 31, 2026Total coliform under 10 · E. coli under 10
- Monday, Aug 24, 2026Total coliform 10 · E. coli under 10
- Monday, Aug 17, 2026Total coliform 41 · E. coli 10
- Monday, Aug 10, 2026Total coliform 121 · E. coli 10
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 (Eureka). Limits: California Code of Regulations, Title 17, Section 7958.