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.
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
During the 2018 swim season, Allyn Waterfront Park had good water quality. On July 9, sampling results were in the advisory range, but subsequent sampling showed that bacterial levels had dropped into the safe swimming range. The beach met the swimming standard during all other periods sampled.
Belfair Sate Park
During the 2018 swim season, Belfair State Park had excellent water quality and met the swimming standard during all periods sampled.
Potlatch State Park
During the 2018 swim season, Potlatch State Park beach had excellent water quality. This beach met the swimming standards for all periods sampled.
Twanoh State Park
Twanoh State Park beach is heavily used during the summer months. During the 2018 swim season, this beach had very good water quality. Twanoh State Park beach 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 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 |