The three major rivers draining Connecticut flow southward to Long Island Sound. The Connecticut River, New England’s longest river, flows southward from Massachusetts to enter Long Island Sound at Old Saybrook. The mouth of the river valley is a deep estuary about 20 miles (30 km) long. The Housatonic River, the only other river that crosses the entire breadth of the state, enters Connecticut in the northwest, near Canaan, and then winds across the Western Highland to the sound. Its principal tributary is the Naugatuck, which joins the main stream at Derby. The Thames River flows into Long Island Sound at New London. A long tidal estuary, the Thames forms the mouth of the Yantic and Shetucket rivers. Those two rivers, together with the Quinebaug, the Willimantic, and the Natchaug, which are tributaries of the Shetucket, are the principal rivers of the Eastern Highland. In addition, numerous short streams, unrelated to the three major river systems, drain the south. Connecticut has about 6,000 lakes and ponds. The largest, Lake Candlewood in the Western Highland, is a reservoir that covers only 9 sq miles. The largest natural lake, Bantam Lake, also in the Western Highland, covers less than 2 sq miles.