The Eramosa River is a river in Wellington County

Wellington County, Ontario

Wellington County is a county located in Southwestern Ontario, Canada. The county seat is Guelph, a city which is politically independent, but Guelph's status as the seat means it houses the county's administrative offices...

 in western Ontario

Ontario

Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

 which rises near Erin, Ontario

Erin, Ontario

Erin is a town in Wellington County, approximately 80 kilometres northwest of Toronto, Ontario, Canada. Erin is an amalgamated town, composed of the former Villages of Erin and Hillsburgh, and the hamlets of Ballinafad, Brisbane, Cedar Valley, Crewson's Corners, and Orton, as well as the former...

 and flows southwest through the city of Guelph

Guelph

Guelph is a city in Ontario, Canada.Guelph may also refer to:* Guelph , consisting of the City of Guelph, Ontario* Guelph , as the above* University of Guelph, in the same city...

, where it joins the Speed River

Speed River

The Speed River is a river that flows through Wellington County and the Region of Waterloo in western Ontario, Canada. It flows south from its source near Orton, through Guelph, where it is joined by the Eramosa River, then through the towns of Hespeler and Preston, finally uniting with the Grand...

, which then enters the Grand River

Grand River (Ontario)

The Grand River is a large river in southwestern Ontario, Canada. From its source, it flows south through Grand Valley, Fergus, Elora, Waterloo, Kitchener, Cambridge, Paris, Brantford, Caledonia, and Cayuga before emptying into the north shore of Lake Erie south of Dunnville at Port Maitland...

 in Cambridge

Cambridge, Ontario

Cambridge is a city located in Southern Ontario at the confluence of the Grand and Speed rivers in the Regional Municipality of Waterloo, Ontario, Canada. It is an amalgamation of the City of Galt, the towns of Preston and Hespeler, and the hamlet of Blair.Galt covers the largest portion of...

.
The river flows through an area covered with several hundred glacial potholes near Rockwood, one of the largest being the Devil's Well, 13.1 metres (43 ft) deep, 6.4 metres (21 ft) wide at the top and 4.9 metres (16.1 ft) at its base.