A watershed is an area of land where all the water—like rain, snowmelt, and streams—drains into a common body of water, such as a river, lake, or ocean. Learn more about watersheds here.

Canada’s freshwater systems are structured in a natural hierarchy of watersheds. Water across the country flows into five major drainage basins, directing water north (the Arctic Ocean, Hudson Bay), east  (Atlantic), west (Pacific) and south (Gulf of Mexico). These drainage basins break down further into 11 major watersheds, which in turn divide into 164 subwatersheds and 974 sub-sub watersheds.

In our assessment, we’ve evaluated freshwater health at every level: from the 5 major basins to the 11 watersheds, all the way down to the 164 subwatersheds.

While local-scale insights provide the most actionable data, it is also essential to evaluate freshwater health at a national level. By examining trends across multiple scales, we can better understand the broader challenges and successes in water management across Canada.

Each watershed in Canada receives a freshwater health score based on four key indicators: water quality, hydrology (water flow), fish populations, and benthic invertebrates. These scores offer critical insight into the health of Canada’s rivers and streams, where data exists, is accessible, and usable. However, one of the most striking findings of this assessment is how much remains unknown. Across the 11 major watersheds, 72% were classified as data deficient, meaning insufficient information was available to confidently assess their overall health. The pattern is similar at the sub-watershed level: 75.6% of Canada’s 164 sub-watersheds are data deficient. While some watersheds scored “Good” or “Very Good”—notably, 9.1% of major watersheds and 19% of sub-watersheds achieved these ratings—the prevalence of data deficiency highlights an urgent gap in long-term, accessible freshwater monitoring.

But identifying these gaps is part of the story. Each watershed’s score is paired with a data sufficiency rating, making it clear where data is robust and where caution is needed. This isn’t just a limitation—it’s a roadmap. By showing where water quality, hydrology, fish, and benthic invertebrates data are lacking, the assessment points to specific regions and indicators that need focused attention. In particular, fish data and benthic invertebrate data were often the most incomplete—over 86% of sub-watersheds lacked sufficient fish data, and nearly 69% lacked benthic scores due to data limitations as well as a a lack of appropriate tolerance values for certain regions, making it impossible to generate reliable scores.

Recognizing these deficiencies is crucial: it allows us to better target future investments, strengthen community and institutional monitoring efforts, helping ensure that even historically under-monitored or remote regions aren’t left out of future freshwater health efforts.