Rio del Mar Beach

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

Common questions.

Is Rio del Mar Beach safe to swim today?

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Rio del Mar Beach is currently safe for swimming. Recent samples within safe ranges.

When was Rio del Mar Beach last tested?

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The most recent water-quality sample at Rio del Mar 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 Rio del Mar Beach?

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The latest reading at Rio del Mar Beach shows 30-day enterococcus geomean at 17 MPN/100mL (EPA geomean limit: 35); enterococcus at 10 MPN/100mL (EPA single-sample limit: 104); and E. coli at 10 MPN/100mL (EPA single-sample limit: 235).

Does rain affect water quality at Rio del Mar 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 Rio del Mar Beach located?

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Rio del Mar Beach is located in the Bay Area area of the San Francisco Bay region (coordinates: 36.9688°N, 121.9060°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 Rio del Mar 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.