Erie, Lake, fourth largest of the five Great Lakes of east-central North America. Slightly less than half of its area of 9,910 square miles (25,667 km2) lies within the United States; the remainder is in Canada. Lake Erie extends 241 miles (388 km) east-west and has a maximum width (north-south) of 57 miles (92 km). It is the shallowest of the Great Lakes, with an average depth of less than 60 feet (18 m); the deepest point is 210 feet (64 m). Lake Erie's surface lies 570 feet (174 m) above sea level.

The lake is part of the Great Lakes-St. Lawrence Seaway system, through which ships sail between the Atlantic Ocean and all parts of the Great Lakes. The Detroit River, Lake St. Clair, and the St. Clair River link Lake Erie with the upper lakes (Huron, Michigan, and Superior); the Niagara River drains Lake Erie into Lake Ontario. Canada's Welland Canal bypasses Niagara Falls. Chief ports on Lake Erie are Ashtabula, Buffalo, Cleveland, Erie, and Toledo in the United States; and Port Colborne and Port Stanley in Canada. Because of its relatively small size and shallow depth, and the heavy urban and industrial concentrations along its shores, Lake Erie is the most severely polluted of the Great Lakes. Since the 1960's pollution control efforts have achieved considerable improvement in water quality; however, pollution remains a problem.

During his travels in 1669, Louis Joliet was probably the first European to see Lake Erie. In the War of 1812, a United States naval force commanded by Oliver Hazard Perry won a decisive battle against the British on Lake Erie. After the Erie and Welland canals opened in the 1820's, commercial traffic on the lake expanded and ports developed. Shipping increased further after the St. Lawrence Seaway opened in 1959.