The Kalamazoo River is a river in the U.S. state of Michigan. The river is 130 miles (210 km) long from the junction of its North and South branches to its mouth at Lake Michigan, with a total length extending to 178 miles (286 km) when one includes the South Branch. The river's watershed drains an area of approximately 2,020 square miles (5,200 km2) and drains portions of ten counties in southwest Michigan: Allegan, Barry, Eaton, Van Buren, Kalamazoo, Calhoun, Jackson, Hillsdale, Kent and Ottawa. The river has a median flow of 1,863 cubic feet per second (52.8 m3/s) at New Richmond, upstream from its mouth at Saugatuck and Douglas.

Lake Michigan is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume and the third-largest by surface area, after Lake Superior and Lake Huron. To the east, its basin is conjoined with that of Lake Huron through the 3+1⁄2-mile (5.6-kilometer) wide, 295-foot deep Straits of Mackinac, giving it the same surface elevation as its easterly counterpart; geologically, the two bodies are a single lake that is, by area, the largest freshwater lake in the world.