Mann Creek Reservoir 15 miles north of Weiser off US 95 in Washington County, foothills Located in Washington County about 15 miles north of Weiser, the reservoir is formed by the Mann Creek Dam offering 250-acres and 5 miles of shoreline. Fishing and boating are the major recreation activities here with wonderful views of the surrounding Hitt Mountains. Restrooms, campsites, boat ramps, and swimming are available at the site. Rainbow, crappie, and largemouth bass are stocked in the water. Restrooms, campsites, boat ramps, and swimming.