Mason County annual BEACH report

Four beaches in Mason County were sampled during 2017. They were:

  • Allyn Waterfront Park
  • Potlatch State Park
  • Twanoh State Park
  • Walker County Park

All Mason County beaches met swimming standards. However, Walker County Park beach has a permanent swim advisory due to a nearby sewage outfall. Details on each beach are presented in the text below.

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.

During the 2017 beach season, 62 public beaches on coastlines were sampled from Memorial Day through Labor Day. High-use beaches were sampled weekly or biweekly for enterococcus, a type of fecal bacteria. High enterococcus levels are linked to swimmer illness.

Mason County swimming beaches

We monitored four beaches in Mason County from May 22 through Sept. 1, 2017. All beaches were sampled weekly except for Walker County Park beach, which was sampled every other week. Details on each beach are presented in the text below.

Allyn Waterfront Park beach

During the 2017 swim season, Allyn Waterfront Park beach had two sampling events where results exceeded the safe swimming standard. On June 19 results were in the advisory range. Subsequent sampling on June 21 showed that bacterial levels had elevated into the closure range resulting in a closure being issued at this beach. All other periods of sampling met the swimming standards.

Potlatch State Park beach

Potlatch State Park beach had excellent water quality and met the swimming standards during all periods sampled.

Twanoh State Park beach

Twanoh State Park beach is heavily used during the summer months. During the 2017 swim season, this beach had very good water quality. Twanoh State Park beach met the swimming standards for all periods sampled.

Walker County Park beach

Walker County Park beach was sampled every other week during the swim season. This beach has a permanent swim advisory due to proximity to a sewage treatment plant outfall. During the 2017 swim season, Walker County Park beach had excellent water quality and met the swimming standards for all periods sampled.

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 2017
Beach Geometric Mean Statistical Threshold Value
Allyn Waterfront Park 22 92
Potlatch State Park 10 14
Twanoh State Park 11 23
Walker County Park 10 15