Oneida Lake is the largest lake entirely within New York state, with a surface area of 79.8 square miles (207 km2). The lake is located northeast of Syracuse and near the Great Lakes. It feeds the Oneida River, a tributary of the Oswego River, which flows into Lake Ontario. From the earliest times until the opening of the Erie Canal in 1825, the lake was part of an important waterway connecting the Atlantic seaboard of North America to the continental interior. The lake is about 21 miles (34 km) long and about 5 miles (8.0 km) wide with an average depth of 22 feet (6.7 m). The shoreline is about 55 miles (89 km). Portions of six counties and sixty-nine communities are in the watershed. Because it is shallow, it is warmer than the deeper Finger Lakes in summer, and its surface freezes solidly in winter. It is relatively safe and popular for the winter sports of ice fishing and snowmobiling.