The river is believed to take its name from its Ojibwa name gisinaa nibiish, which means "cold pool of water".

The Coldwater River begins at the outflow from a small dammed lake, next to Ontario Highway 400, at Martinville in the municipality of Oro-Medonte and adjacent to the Oro Moraine.

The lake was created as part of the Copeland Forest Resource Management Area by Ducks Unlimited.

[2] It heads northeast to the community of Eady, then north north-west to the eponymous community of Coldwater in the incorporated township of Severn, where it is crossed by Ontario Highway 12, at this point part of the Trans-Canada Highway.

The river valley is used as a route by both Ontario Highway 400 and by the Canadian Pacific Railway transcontinental main line, Mactier Subdivision.