Quaddick Reservoir, Reservoir in Thompson, Connecticut, United States

Quaddick Reservoir is a large body of water created by damming the Five Mile River, spreading across about 408 acres in Thompson. The water averages 2.5 meters deep, is fed by several streams, and contains over twenty aquatic plant species ranging from native water lilies and bladderwort to invasive watermilfoil and fanwort.

The reservoir was created in 1865 by damming the Five Mile River and originally powered mills and industries in Thompson through waterpower. Over time it shifted from an industrial site to a place for outdoor recreation and continues to manage water levels for the surrounding area.

The name Quaddick is of Native American origin, commonly rendered as 'long pond' or 'slow-moving water'. The reservoir's three sections, Lower, Middle and Upper, are used today for fishing, boating and swimming, with Quaddick State Park on the eastern shore of the Middle section. The Quaddick Lake Association works with the Connecticut Department of Energy and Environmental Protection on the lake's care.

Quaddick State Park on the eastern shore of the Middle Reservoir provides a public beach, boat launch, and hiking trails. The reservoir's three sections—Lower, Middle, and Upper—are reached from Quaddick Road. The water level is drawn down in winter, exposing shoreline mudflats.

The reservoir's three sections are individually named: Lower covers 124 acres, Middle 203 acres, and Upper 81 acres. Quaddick State Park occupies the eastern shore of the Middle section. The reservoir sits at 123 meters above sea level, and Quaddick Mountain rises nearby.