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Note: This data has been replaced by the Ontario Watershed Boundaries (OWB).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.

For more information

Provincial Mapping Unit  |


Data Available

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2010-01-01 - 2015-03-01

Supporting Files

Additional Info

Field Value
Geographic coverage Ontario
Geography Breakdown Watershed
Source URL/Address
Maintainer Provincial Mapping Unit
Author Provincial Mapping Unit
Author Email Provincial Mapping Unit
Maintainer branch Mapping and Information Resources Branch
Last Validated Date 2021-06-07
Update frequency Never
Access instructions