It is located in the south central part of the province in a region called the Prairie Pothole Region of North America, which extends throughout three Canadian provinces and five U.S. states.

The Arm River starts in the south-east corner of the Allan Hills in the RM of McCraney, near Horseshoe Lake.

From Arm Lake, it parallels Highway 11 in a south-east direction through a valley that was formed during the last ice age over 11,000 years ago.

[8] The original dam across the river was built about 500 metres (1,600 ft) north of the current dam by the Canadian National Railway (CNR) in the early 1900s to supply water for the trains.

It is located at a bend in the river about halfway between Chamberlain and Findlater in the RM of Sarnia No.