The Pine River is a river in the Lower Peninsula of the U.S. state of Michigan. The Pine River is a tributary of the Chippewa River and is thus part of the Saginaw River drainage basin.
The river rises in Wheatland Township in southeast Mecosta County at . It flows southeast into southwest Isabella County. It turns south through northeast Montcalm County and Gratiot County, where it turns to the northeast, continuing through the cities of Alma and St. Louis. It enters Midland County and joins the Chippewa River at approximately two miles before the Chippewa joins the Tittabawassee River on the west side of the city of Midland.
The river was contaminated by the Michigan Chemical Corporation (later Velsicol Chemical Corporation) in St. Louis and has been subject to extensive clean-up efforts.