Lake Kilby is the oldest of the Portsmouth water supply lakes. It is a colonial era millpond. The upper half of this 222-acre is a dense and very scenic cypress swamp. The water is dark-tannin stained and slightly acidic. Under these conditions, fishes such as flier, warmouth, chain pickerel, and black crappie flourish. Other sport fishes in Kilby include bluegill, redear, and largemouth bass. Population sampling has shown that these fisheries are well balanced and perhaps most notable for the large "bream."