The river begins at Swallow Lake[2] and flows south east then east, passing through Matawin River Provincial Park[3][4] The river heads northeast, passes into geographic Sackville Township,[5] then geographic Laurie Township, passes over a concrete weir built in 1969 (replacing a "…wooden weir built by the Great Lakes Paper Company in the 1930s for use in their log drives.

")[6] that helps to regulate water flow further downstream, passes over a series of falls called McGraw Falls, enters geographic Horne Township,[7] and takes in the left tributary Shebandowan River.

From this point downstream to the mouth, the river is paralleled by the Canadian National Railway (CN) main line (originally the Canadian Northern Railway transcontinental main line).

The river continues east, takes in the right tributary Wiegand River, passes through the northwest corner of the municipality of Conmee,[8] enters geographic Dawson Road Lots Township,[9] and reaches the community of Sunshine.

There, the river is crossed by the concurrent Ontario Highway 11 and Ontario Highway 17, at this point part of the Trans-Canada Highway, and the Canadian Pacific Railway transcontinental main line, and just further downstream at the railway point of Conmee[10] by the CN Graham Subdivision main line (originally built as part of the National Transcontinental Railway), now abandoned.