East GTA Watersheds

Watersheds in the East Greater Toronto Area are interesting, given that the urban area is aligned closer to the shore, and the watersheds are bounded by the Oak Ridges Moraine to the north.

There are 5 main watersheds that are home to the largest watercourses: Duffins, Harmony-Farewell, Lynde, Oshawa and Bowmanville Creeks. Altogether, they make up 63% of urban Durham Region. These watersheds also have significant catchments upstream of the urban boundary, with 20-70% of the total watershed above the urban boundary.

There are another 10 smaller watersheds wedged between then that are less than 4,000 hectares: Carruthers, Pringle, Petticoat, Darlington, Corbett, Tooley, Wilmot, Robinson, Westside and Graham Creeks. These make up another quarter of urban Durham, and half of their total catchments are rural.

The interstitial drainage areas between make up another 11% of the urban area. 12 of the 14 areas cover less than 1,000 hectares each. Two exceptions to this are Frenchman’s Bay, which covers over 2,700 hectares, as well as the Rouge River, which despite being the Region’s largest watershed, only has 1% of its catchment within Ajax’s southwest corner.

The map below shows the boundaries of these watersheds. Overtop of that, I have mapped the numerous watercourses within them.

This is a work in progress. See a mapping error? Have a name to put to an unnamed tributary? Please feel free to send me comments.

Notes and Disclaimers

This data was created with the support of roadway, natural feature, and administrative boundary data from various open data portals, as well as hydology and digital terrain information from the Ontario GeoHub, made available under the Open Government Licence – Ontario Licence v1.0.
This is interpretive and not based on a full qualified assessment of surface and groundwater resources. Therefore this data is provided ‘as is’; please refer to additional disclaimers at the Open Data page.
While this page advocates for greater public access, not all watercourses are publicly accessible. Please observe all signage respecting access and refrain from travelling off established trails, for your health and safety, as well as the integrity of local ecosystems.