Upper Stillwater Reservoir, Reservoir in Duchesne County, Utah, USA

Upper Stillwater Reservoir is a reservoir in Duchesne County, Utah, on the south slope of the High Uintas, formed in 1987 by the concrete Upper Stillwater Dam. The dam is a roller-compacted concrete gravity structure with a stepped spillway. The reservoir sits at 8,176 ft and has a mean depth of 103.5 ft. Two campgrounds, Rock Creek and Upper Stillwater, are nearby.

The Upper Stillwater Dam was completed in 1987, creating the reservoir as a major water management project in Utah's mountains. Built with a stepped spillway design, it was developed to store water for agricultural irrigation across the region and nearby communities on the Wasatch Front.

The managed recreation season runs June through September, with the heaviest use on holidays and weekends. Two campgrounds serve the area: Rock Creek and Upper Stillwater Campground. The High Uintas Wilderness boundary lies about one mile north of the dam, near the reservoir's high water line, so hikers and horseback riders can enter the wilderness directly from the trailhead.

The dam's stepped spillway is designed so that in years of heavy snow or fast melt, water pours over it as a curtain 600 feet wide and 200 feet tall. The overflow usually lasts only a few days and draws tourists and media. The spillway sits near the High Uintas Wilderness boundary, about a mile north of the dam.