The Nith river begins in a woodland northwest of Crosshill and west of Waterloo Regional Road 5 in the township of Wellesley, Region of Waterloo. It heads north into Perth County, then turns sharply southwest and passes through the communities of Fernbank and Millbank in Perth East. It continues south, takes in the righttributarySmith Creek and arrives at the community of Nithburg. The river flows east back into Waterloo Region, takes in the right tributarySilver Creek, and then the left tributary Firella Creek south of the community of Wellesley in the township of Wellesley. The river turns south into the township of Wilmot, takes in the left tributary Bamberg Creek and passes through the communities of Phillipsburg and New Hamburg, Ontario. The Nith continues south, takes in the left tributaries Baden Creek and Hunsburger Creek, enters into Blandford-Blenheim, Oxford County and reaches the community of Plattsville. The river turns east, takes in the right tributary Black Creek, and left tributaries Hiller Creek, Alder Creek and Eden Creek, passes back into Waterloo Region, and reaches the community of Ayr in the township of North Dumfries, where it takes in the left tributary Cedar Creek. It then turns sharply west, flows back into Oxford County, then turns southeast passing through the communities of Wolverton and Canning. The Nith then flows into Brant County, takes in the right tributary Mud Creek and left tributary Charlie Creek, passing Barker's Bush and reaching its mouth at the Grand River in Paris.
Recreation
The Nith River is flat water with a few riffles, but rain and snowmelt can significantly increase the flow rate. In the early spring the maximum flow rate reaches a median value of 30 and mean of 40, but commonly exceeds 200 m3/s, causing major flooding in the flat regions upstream such as in and around New Hamburg. The Nith offers excellent paddling conditions in April, including a set of Class III whitewater rapids as the Nith enters Paris, yet by May, the flow rate drops below 5 m3/s and becomes unsuitable for paddling. The river is under the auspices of the Grand River Conservation Authority.
