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A watershed is an area that drains all precipitation received as a runoff or base flow (groundwater sources) into a particular river or set of rivers. The easiest way to describe the network of rivers and lakes on a small-scale map is to show the watersheds. In Canada, there is a detailed hierarchy of watersheds, ranging from the largest (drainage into oceans and their equivalents), down to the smallest ramification. Canada’s ocean watersheds are the Atlantic Ocean, Hudson Bay, Arctic Ocean, Pacific Ocean and Gulf of Mexico.

A drainage basin is an area that drains all precipitation received as a runoff or base flow (groundwater sources) into a particular river or set of rivers. Canada’s major drainage regions are the Atlantic Ocean, Hudson Bay, Arctic Ocean, Pacific Ocean and Gulf of Mexico. Rivers are organized into networks, each with its own recharge area upstream, and drainage channel and mouth downstream. Networks are ordered from ocean to main river to secondary rivers to streams which correspond to ocean basins, river basins, sub-basins, sub-sub-basins, and so forth.

Contained within the Atlas of Canada 8.5x11 series maps is a map which was created as a joint effort by The Atlas of Canada, The National Institute of Statistics, Geography and Informatics, Mexico and the National Atlas of the United States under the sponsorship of the commission for environmental cooperation. The map shows the major North American drainage basins, or wateresheds, which drain into the Atlantic Ocean, Hudson Bay, the Arctic Ocean, the Pacific Ocean, the gulf of Mexico and teh Caribbean Sea. Each watershed is shown in its own colour, with subdivisions shown in tonal variations. Areas of internal drainage, which lack outlets to the sea, are shown in grey.

A drainage basin is the area that drains all precipitation into a river or stream system into a common outlet such as a lake or sea. There are two main river basins in Nunavut: the Thelon River flows into Hudson Bay and the Back River empties into the Arctic Ocean. Most of Nunavut’s area is not drained through large rivers; instead the water flows directly to the ocean through small rivers and streams.

The “Major Drainage Systems of the AAFC Watersheds Project - 2013” dataset is a geospatial data layer containing polygon features representing the three (3) major drainage system basins of the Agriculture and Agri-Food Canada (AAFC) Watersheds Project. The Project area has been split according into which body of water it drains: the Arctic Ocean, Hudson Bay or Gulf of Mexico.

This map shows the five major ocean drainage areas in Canada: Hudson Bay, Arctic Ocean, Atlantic Ocean, Pacific Ocean and Gulf of Mexico. An inset map shows the major dams with reservoir capacity larger than 1 billion cubic metres. Six of the 10 largest hydro-electric generating stations by capacity are located in the province of Quebec; whereas, the largest, Churchill Falls is in Newfoundland and Labrador. The other 3 are located in British Columbia.

Contained within the Atlas of Canada Poster Map Series, is a map depicting the 5 main watersheds in Canada. Building Canadian Water Connections initiative and the Canadian Wildlife Federation have collaborated to produce this map that promotes the importance of watersheds through education. Canada's five ocean watersheds are colour-coded on the map: Pacific Ocean, Arctic Ocean, Hudson Bay, Atlantic Ocean and Gulf of Mexico. Each of these five massive landscapes contains a hierarchy of watersheds.

Contained within the 4th Edition (1974) of the Atlas of Canada is a map that shows drainage basins as well as major lakes and diversions. The map displays the ocean drainage areas along with component river basins and diversion areas for the Arctic, Pacific, Hudson Bay and Atlantic drainage areas.

Contained within the 2nd Edition (1915) of the Atlas of Canada is a map that shows the delineation of drainage basin. The total area drained is indicated in square miles for each basin, and drainage basins of the principal river systems of Canada, along with their areas. This includes the great oceanic drainage basins and the Hudson Bay basin. Only the Canadian drainage area is indicated on the map for basins that lie partly in the United States.

The current and most detailed version of the approved corporate provincial digital Biogeoclimatic Ecosystem Classification (BEC) Zone/Subzone/Variant/Phase map (version 11, August 10th, 2018). Use this version when performing GIS analysis regardless of scale. This mapping is deliberately extended across the ocean, lakes, glaciers, etc to facilitate intersection with a terrestrial landcover layer of your choice