| Mystery Bay Marine State Park | |
| Map: | Strait of Juan de Fuca#USA Washington#USA |
| Map Size: | 280 |
| Relief: | 1 |
| Location: | Jefferson, Washington, United States |
| Coordinates: | 48.0589°N -122.6944°W |
| Area Acre: | 18 |
| Elevation: | 16feet |
| Established: | 1972 |
| Operator: | Washington State Parks and Recreation Commission |
| Website: | Mystery Bay Marine State Park |
Mystery Bay State Park is an 18acres Washington marine state park on Mystery Bay, a small inlet off Scow Bay/Kilisut Harbor on the western side of Marrowstone Island. The park is located approximately one-half mile north of the Nordland General Store (which also faces Mystery Bay) on Flagler Road (SR 116). Many older wooden sailboats can be swinging at permanent moorage at the park. Park activities include picnicking, shellfish harvesting, fishing, boating, beachcombing, and scuba diving.