Provincial Watersheds, Historical

Note: This data has been replaced by the Ontario Watershed Boundaries (OWB). We are no longer updating this data. It is best suited for historical research and analysis.

A watershed, also known as a catchment basin, includes all land that is drained by a watercourse and its tributaries.

Watersheds are split into four categories:

primary
secondary
tertiary
quaternary

These divisions are based on the federal framework originally known as the Water Resources Index Inventory Filing System.

Ontario has 3 primary watersheds:

Great Lakes – St. Lawrence
Southwestern Hudson Bay
Nelson River

Secondary watersheds are subdivisions of primary watersheds in Ontario. Most secondary divisions are either large river systems or groupings of small coastal streams.

Tertiary watersheds are subdivisions of secondary watersheds in Ontario.

Quaternary watersheds are subdivisions of tertiary watersheds. There are more than 1000 quaternary watersheds in Ontario.

Ministry contact: Provincial Mapping Unit

Additional information

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watershed watershed
Geographic coverage: Ontario
Geography Breakdown: Watershed
Maintainer: Provincial Mapping Unit
Author: Provincial Mapping Unit
Maintainer branch: Mapping and Information Resources Branch
Last Validated Date: June 7, 2021
Update frequency: Never