Station O100 (Rio del Mar, California)

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

Common questions.

Is Station O100 (Rio del Mar, California) safe to swim today?

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Station O100 (Rio del Mar, California) is currently inconclusive for swimming. Last sample is over 30 days old — too stale to be a reliable swim-safety indicator.

When was Station O100 (Rio del Mar, California) last tested?

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The most recent water-quality sample at Station O100 (Rio del Mar, California) was collected on Mar 4, 2026 (90 days ago). California monitoring agencies test Bay Area beaches weekly during swim season (roughly May through October).

What is the bacteria level at Station O100 (Rio del Mar, California)?

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The latest reading at Station O100 (Rio del Mar, California) shows 30-day enterococcus geomean at 10 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 Station O100 (Rio del Mar, California)?

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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 Station O100 (Rio del Mar, California) located?

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Station O100 (Rio del Mar, California) is located in the Bay Area area of the San Francisco Bay region (coordinates: 36.9617°N, 121.8957°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 Station O100 (Rio del Mar, California) 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.