Mason County annual BEACH report

We monitored three beaches weekly in Mason County during the 2022 season:

  • Belfair State Park
  • Potlatch State Park
  • Twanoh State Park


Twanoh State Park Beach in Mason County

Keeping beaches safe

The Beach Environmental Assessment, Communication & Health, or BEACH, Program ensures that marine water is safe to swim and play in and informs the public if water doesn't meet swimming standards. Sampling takes place from Memorial Day to Labor Day. During this time, you can check out current water quality conditions on the swimming map.  

Our agency BEACH staff sampled three beaches weekly in Mason County during the 2022 season.

See details on each beach below.

Data summary: Bacteria results compared to standards

The chart below summarizes the bacteria levels at Mason County beaches in relation to the EPA swimming standard or saltwater swimming criteria. Beaches are considered unsafe for swimming when the geometric mean of enterococcus/100 mL of water is greater than or equal to 30 and the statistical threshold value of enterococcus/100 mL is greater than or equal to 110. We issue a public swimming advisory when enterococcus levels exceed 104 per 100 mL of water. 

Table: Calculated geometric mean and statistical threshold value at Mason County beaches (in enterococcus per 100 mL) for 2022.

Beach GM STV
Belfair State Park 14 37
Potlatch State Park 10 14
Twanoh State Park 16 56