Main Beach

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

Common questions.

Is Main Beach safe to swim today?

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Main Beach is currently not safe for swimming. One or more bacteria readings exceeded EPA thresholds in the most recent sample. See the readings below for which indicator and how far above the limit.

When was Main Beach last tested?

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The most recent water-quality sample at Main Beach was collected on May 19, 2026 (14 days ago). California monitoring agencies test Bay Area beaches weekly during swim season (roughly May through October).

What is the bacteria level at Main Beach?

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The latest reading at Main Beach shows 30-day enterococcus geomean at 35 MPN/100mL (EPA geomean limit: 35); enterococcus at 20 MPN/100mL (EPA single-sample limit: 104); and E. coli at 30 MPN/100mL (EPA single-sample limit: 235).

Does rain affect water quality at Main 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 Main Beach located?

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Main Beach is located in the Bay Area area of the San Francisco Bay region (coordinates: 36.9628°N, 122.0200°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 Main 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.