Although natural in origin, the surface elevation of the lake has been raised by a small concrete and masonry dam. The surface area of the lake is approximately. The lake has a maximum depth of, an average depth of, and contains approximately of water. The lake is fed by Sucker Brook, numerous small streams, and groundwater that enters through the lake bottom. Drainage from Waramaug Lake flows southward into the East Aspetuck River. The bottom materials on steep side slopes of the lake consist primarily of gravel, cobbles, and boulders, whereas the flatter areas consist primarily of sand, mud, and organic muck. The watershed of the lake is 14.4 square miles. Approximately 74 percent of the watershed is forested. Wetlands and water bodies comprise approximately 10 percent of the watershed, while the remaining 16 percent of the area is low-density residential housing and commercial and agricultural land. The shoreline development of Lake Waramaug is moderate and includes houses, seasonal cottages, and boat houses, with few commercial establishments. Public access to the lake is available only within Lake Waramaug State Park, which is located at the northwestern end of the lake. Outside park boundaries, the shoreline is privately owned. The park can be reached by taking Route 45 north from Route 202 and turning west onto North Shore Road. An aquatic survey of Waramaug Lake was published in 1987. The survey found aquatic vegetation to be relatively sparse, with only localized growths of emergent and submergent species along the shorelines and shallows of the lake. Aquatic species observed include Robbins pondweed, coontail, white-water lily, narrow-leaved arrowhead, yellow-pond lily, spike rush, bushy pondweed, leafy pondweed and pondweed. The fish species observed in Waramaug Lake include largemouth, smallmouth and calico bass; lake and rainbow trout; yellow and white perch; pickerel, alewives, sunfish, and bullheads.
In 2004, the Town of Washington entered into an agreement with the Connecticut Department of Environmental Protection to reconstruct and expand the town's boat launch at Lake Waramaug, and to permit 20 launchings per day by non-residents in exchange for the DEP agreeing not to construct a new boat launch at Lake Waramaug State Park. The agreement limits motor boat traffic on the lake, and requires inspection of all boats for invasive aquatic plant species prior to launching. Plans for the new boat launch were developed in 2006, and the new facility was opened in 2008. In 2010, the Town of Washington separately completed major reconstruction of the adjacent, hitherto forlorn town beach at Lake Waramaug, which may be used only by Washington residents and their guests. New parking areas were constructed, new fencing and landscaping were installed, and a new boathouse with a caretaker's apartment was constructed.
