what county is mason lake in
Larger Map. Mason Lake is a natural freshwater lake with an elongated shape located in Mason County, part of Washington state's Olympic Peninsula tourism region. Mason Lake is the largest and deepest lake in Mason County, which boasts a total of 118 lakes. With its steep, rocky shoreline, Mason Lake is a favorite fishing location for largemouth bass, yellow perch, rock bass, and cutthroat trout.