The Magnetawan River is a river in Parry Sound District, Ontario which flows 175 km from Algonquin Park to empty into Georgian Bay at the town of Britt, Ontario on Byng Inlet.

At the end of the 19th century, the river was used to float white pine logs to sawmills downstream.

The town of Magnetawan, Ontario is located on the river between Lake Cecebe and Ahmic Lake. Locks were built on the river here to allow steamboats to travel further down the river from the railway station at Burk's Falls.

The name of the river means "long open channel" in the Ojibwa language.