Lake Natoma at Nimbus Flat north beach

Each dot is one sample taken by the monitoring agency. Dashed lines mark each indicator's EPA single-sample limit; bars along the bottom show daily rainfall.

Common questions.

Is Lake Natoma at Nimbus Flat north beach safe to swim today?

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Lake Natoma at Nimbus Flat north beach is currently inconclusive for swimming. Last sample is over 30 days old — too stale to be a reliable swim-safety indicator.

When was Lake Natoma at Nimbus Flat north beach last tested?

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The most recent water-quality sample at Lake Natoma at Nimbus Flat north beach was collected on Aug 18, 2026 (35 days ago). California monitoring agencies test Bay Area beaches weekly during swim season (roughly May through October).

What is the bacteria level at Lake Natoma at Nimbus Flat north beach?

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The latest reading at Lake Natoma at Nimbus Flat north beach shows E. coli at 21 MPN/100mL (EPA single-sample limit: 235).

Does rain affect water quality at Lake Natoma at Nimbus Flat north 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 0.01 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 Lake Natoma at Nimbus Flat north beach located?

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Lake Natoma at Nimbus Flat north beach is located in the Bay Area area of the San Francisco Bay region (coordinates: 38.6367°N, 121.2154°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 Lake Natoma at Nimbus Flat north 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.