This product provides the boundaries for the 25 drainage regions in Canada and the five ocean drainage areas. These drainage regions cover all of the area within the coastal boundaries of Canada.

The drainage regions were developed to provide a good representation of the hydrology in Canada and can be built up from the sub-sub-drainage area of the Standard Drainage Area Classificaton (SDAC) 2003). 

These files were produced by Statistics Canada, Environment, Energy and Transportation Statistics Division, 2009, special tabulation of data from Pearse, P.H., F. Bertrand and J.W. MacLaren, 1985, Currents of Change: Final Report of the Inquiry on Federal Water Policy, Environment Canada, Ottawa.

These files will also be accessible as web services on the Government of Canada web site Open Maps.

• Classification
• Drainage
• Geographic data
• Rivers
• Surface water
• Water

Please see, https://open.canada.ca/en/open-government-licence-canada 

A drainage basin is an area that drains all precipitation received as either runoff or base flow (groundwater sources) into a particular river or set of rivers. The boundary of a drainage basin is defined as the ridge beyond which water flows in the opposite direction. A drainage basin is also known as a catchment area or a watershed. NRCAN and Stats Canada use the term drainage basin and drainage region interchangeably. 

River flow (discharge) was the critical factor used to delineate basin boundaries. All rivers with an annual mean flow higher than 10 000 cubic feet per second were depicted. However, land areas containing river basins that did not meet this annual mean flow threshold were assigned to the generic category "seaboard". The major river basins are the rivers that directly flow into the ocean. Within each major river basin, up to three levels of component basins were identified. In addition, water diversions larger than 1000 cubic feet per second were mapped. Natural Resources Canada. 1985. Canada--Drainage Basins [map]. National Atlas of Canada, 5th Edition.

Source: https://open.canada.ca/data/en/dataset/b1c2dffa-c2ba-4d0e-b803-a483eef0f579