Lake Michigan is one of the five Great Lakes of North America and the only one located entirely within a single country, the United States. It is the second largest of the Great Lakes by volume and the third largest by surface area, after Lake Superior and Lake Huron (and is slightly smaller than the U.S. state of West Virginia). Hydrologically, the lake is a large bay of Lake Michigan-Huron, having the same surface elevation as Lake Huron (among other shared properties). It is bounded, from west to east, by the U.S. states of Wisconsin, Illinois, Indiana, and Michigan. The word "Michigan" originally referred to the lake itself, and is believed to come from the Ojibwa word mishigami meaning "great water".
Lake Michigan-Huron is geologically the largest of the North American Great Lakes. Traditionally considered to be two separate lakes, Lake Michigan and Lake Huron, it is hydrologically a single body of water connected at the Straits of Mackinac.
The straits are 5 miles (8 km) wide and 120 feet (37 m) deep, small in comparison to the body of water as a whole. The two sections have thus long been considered distinct lakes. However, they lie at the same surface elevation, 577 feet (176 m), rise and fall together, and the flow of water between them at times reverses from eastward to westward. The National Oceanic and Atmospheric Administration states, "Lakes Michigan and Huron are considered to be one lake hydraulically because of their connection through the deep Straits of Mackinac." When providing level information, The United States Army Corps of Engineers says "Lakes Michigan and Huron are considered to be one lake, as they rise and fall together due to their union at the Straits of Mackinac."
At 45,410 square miles (117,600 km2), Lake Michigan-Huron is the largest of the Great Lakes in terms of surface area, being 48% of the total, and is the largest lake in the world after the Caspian Sea. (The Caspian is generally regarded as a saline lake, but is also regarded as a sea; geologically it is oceanic.). Lake Superior holds more water, 3,000 cubic miles (12,500 km3) compared to Michigan-Huron's 2,000 cubic miles (8,300 km3), which makes Michigan-Huron the fourth largest lake by volume in the world after lakes Baikal, Tanganyika, and Superior.