Hidden Beach

Each dot is one sample taken by the monitoring agency. The dashed brick line marks the EPA single-sample limit.

Common questions.

Is Hidden Beach safe to swim today?

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Hidden Beach is currently safe for swimming. Recent samples within safe ranges.

When was Hidden Beach last tested?

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The most recent water-quality sample at Hidden Beach was collected on May 20, 2026 (13 days ago). California monitoring agencies test Bay Area beaches weekly during swim season (roughly May through October).

What is the bacteria level at Hidden Beach?

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The latest reading at Hidden Beach shows 30-day enterococcus geomean at 31 MPN/100mL (EPA geomean limit: 35); E. coli at 74 MPN/100mL (EPA single-sample limit: 235); and enterococcus at 31 MPN/100mL (EPA single-sample limit: 104).

Does rain affect water quality at Hidden Beach?

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Yes. Heavy rainfall washes bacteria and pollutants from land into the water, raising contamination risk for 24–72 hours. The past 48 hours recorded 0.00 in of rain; the past 72 hours recorded 0.00 in. Our advisory threshold is ≥1.00 in over 48h (or ≥0.50 in over 72h) for enclosed or storm-drain beaches.

Where is Hidden Beach located?

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Hidden Beach is located in the Bay Area area of the San Francisco Bay region (coordinates: 36.9571°N, 121.8890°W). You can get turn-by-turn directions via Google Maps or Apple Maps directly from this page.

How is the water quality data for Hidden Beach collected?

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Bacteria samples are collected by California state and county health agencies under the AB 411 Safe-to-Swim program and reported to the state's Safe-to-Swim database (data.ca.gov). Rainfall figures come from Open-Meteo forecast and archive data. Bay Area Swim aggregates both sources and updates every morning.