Mason County annual BEACH report

We monitored four beaches in Mason County from May 21 through Aug. 31, 2018:

  • Allyn Waterfront Park
  • Belfair State Park
  • Potlatch State Park
  • Twanoh State Park

All beaches were sampled weekly except for Belfair State Park beach, which was sampled every other week.

Colorful beach umbrellas line a crowded blue-water beach on a sunny day

Twanoh State Park Beach in Mason County

Keeping beaches safe

The Beach Environmental Assessment, Communication & Health (BEACH) Program ensures that marine water is safe to swim and play in and informs the public if water doesn't meet swimming standards.

From Memorial Day through Labor Day in 2018, we sampled 62 public high-use beaches statewide, either weekly or biweekly, for enterococcus, a type of fecal bacteria. High enterococcus levels are linked to swimmer illness.

Mason County saltwater swimming beaches

We monitored four beaches in Mason County from May 21 – Aug. 31, 2018. All beaches were sampled weekly except for Belfair State Park beach which was sampled every other week.

Find details about each of the Mason County beaches below:

Allyn Waterfront Park Belfair Sate Park Potlatch State Park Twanoh State Park

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 35 and the statistical threshold value of enterococcus/100 mL is greater than or equal to 276. We issue a public swimming advisory when enterococcus levels reach 104 per 100 mL of water. 

Table: Calculated geometric mean and statistical threshold value at Mason County beaches (in enterococcus per 100 mL) for 2018

Beach Geometric Mean Statistical Threshold Value
Allyn Waterfront Park 16 43
Belfair State Park 12 19
Potlatch State Park <10 10
Twanoh State Park 11 17