Lake Dillon — officially Dillon Reservoir — is the summer centrepiece of Summit County and sits just a few minutes' drive from Keystone. At 9,017 feet elevation, the reservoir covers nearly 3,300 acres, and the surrounding backdrop of peaks makes it one of the more dramatic settings for water sports in the Rocky Mountains.
Sailing is the main attraction and the Dillon Yacht Club operates one of the highest-altitude marinas in the US. Kayaking, paddleboarding, and windsurfing are also popular, and rentals are available at the Dillon Marina. Swimming is permitted but the water stays cold year-round — typically 55–65°F in summer — so it is brisk by most standards.
The Dillon Reservoir Recreation Area encircles the lake with roughly 27 miles of trail, passable on foot or bicycle. The full loop is a good day's outing with consistent views of the water and surrounding peaks. Trailheads are accessible from Dillon, Frisco, and the Keystone side of the reservoir.
Fishing is productive: the reservoir holds rainbow trout, brown trout, kokanee salmon, and yellow perch. Boat fishing is most effective, though bank access exists at several points. A Colorado fishing licence is required.
The town of Dillon, on the north shore, has a small marina area with outdoor seating restaurants and a farmers' market that runs on Fridays in summer. Frisco, on the west shore, has more shops and a bike path that connects directly to the reservoir trail system.