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 2019, 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 three beaches weekly in Mason County from May 20 – Aug. 30, 2019.
Find details about each of the Mason County beaches below:
During the 2019 swim season, Belfair State Park had very good water quality and met the swimming standard during all periods sampled.
A shoreline survey was conducted at this beach by BEACH Program staff on May 6, 2019.
During the 2019 swim season, Potlatch State Park beach had excellent water quality. This beach met the swimming standards for all periods sampled.
A shoreline survey was conducted at this beach by BEACH Program staff on May 6, 2019.
The Twanoh State Park beach is heavily used during the summer months. During the 2019 swim season, this beach had excellent water quality. Twanoh State Park beach met the swimming standards for all periods sampled.
A shoreline survey was conducted at this beach by BEACH Program staff on May 6, 2019.
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 2019
| Beach |
Geometric Mean |
Statistical Threshold Value |
| Belfair State Park |
13 |
26 |
| Potlatch State Park |
<10 |
11 |
| Twanoh State Park |
<10 |
10 |