Most Marin County beaches received strong water quality grades during the 2025 monitoring season, though the percentage of top-rated beaches fell below the county’s historical average, according to Heal the Bay’s annual Beach Report Card.
The report found that 78% of Marin beaches earned A or B grades during the summer dry season, compared with a five-year average of 97%.
Statewide, 91% of California beaches received A and B grades under similar conditions, the report said.
Marin County officials said the decline was unexpected because lower rainfall is typically associated with better beach water quality. Heal the Bay reported Marin received about 21 inches of rain during the monitoring period, roughly 8% below the 10-year average.
The county monitored 31 recreational water sites from April through October 2025. County officials said the unusual summer trend warrants further investigation.
The report also noted about 55,000 gallons of wastewater reached surface waters in 10 sewage spill incidents during the 2025-26 observation period. Authorities said the spills were promptly reported and addressed by the responsible sanitation districts.
County health officials continue to monitor water quality weekly and advise the public to avoid beaches with posted advisory signs and to stay out of coastal waters for at least three days after heavy rain.