The Saginaw River is a 22.4-mile-long (36.0 km) river in the U.S. state of Michigan. It is formed by the confluence of the Tittabawassee and Shiawassee rivers southwest of Saginaw. It flows northward into the Saginaw Bay of Lake Huron, passing through Bay City, which developed around it in the 19th century. The watershed area is 8,595 square miles (22,260 km2).The river is an important shipping route for Mid-Michigan, passing through the cities of Saginaw and Bay City.