Wa. State 360 Welcome to "The Old Swimming Hole Off-Leash Dog Park." ¶ The city of Manson, Washington has designated The Old Swimming Hole as an Off-Leach Dog Park for socialized dogs. And it is located barely west of the Manson Bay Park. ¶ This photo was captured on New Year's Day 2015 at approximately 300 West Manson Boulevard, Manson, Washington 98831 United States of America.