You’re flowing NORTH into Hudson’s Bay: this is the Nelson River watershed.
The OVERALL health score of the
Nelson River
watershed
is Good
Enough data? Partially sufficient
Stretching from the Rocky Mountains across most of the southern Prairie provinces to northwestern Ontario, the Nelson River watershed ultimately drains into Hudson Bay. Cities within this region include Winnipeg, Regina, Saskatoon, Calgary, and Edmonton.
Did you know? Originating from Lake Winnipeg, the Nelson River watershed drains much of southern Manitoba into Hudson Bay. It plays a key role in Manitoba’s hydroelectric network and is part of one of the largest freshwater drainage systems in North America. The Nelson River region was crucial to the Hudson’s Bay Company fur trade, with York Factory serving as a major trading hub for centuries. Many modern Indigenous communities in Manitoba and northwestern Ontario still depend on the lakes and rivers for fishing and travel.
NATIVE LANDS
Assiniboine, Blackfoot / Niitsítapi, Dakota, Lakota Métis, Plains Cree, Nēhiyawak (Cree), Ĩyãħé Nakón mąkóce (Stoney Nakoda)
JURISDICTION
Manitoba, Ontario, Alberta
POPULATION CENTER(S)
Calgary, AB
WATERSHED SIZE
987,015 km² (~10% of Canada)
POPULATION
~4 million
YEARLY FLOW
100,965 m³/s (that’s ~40 Olympic swimming pools filled per second!)
Summary of results
Very good | Good | Fair | Poor | Very poor | Data deficient | Not scored |
Divided into... | ||||||
|---|---|---|---|---|---|---|
How to interpret the scores
Very good | Good | Fair | Poor | Very poor | Data deficient | Not scored |
Our freshwater health scores are based on four key metrics: water quality, hydrology (flow), benthic macroinvertebrates, and fish populations. For each metric, we use standardized criteria—such as exceedance of federal and provincial water quality guidelines, long-term trends in river flow, tolerance values for invertebrates, and native fish species richness—to assess conditions across watersheds.
To make these scientific results easier to understand, we translate them into a simple 1 to 5 scale: 1 = VERY POOR and 5 = VERY GOOD
These scores provide an overall picture of freshwater health, helping both experts and the public quickly see where attention is needed.
It’s important to remember:
- We calculate scores at a national scale, using the best available data. While this provides a valuable snapshot, it may not capture every local nuance.
- For some regions and specific waterbody types (like northern areas or mud-bottom prairie rivers), certain metrics—like the Hilsenhoff Biotic Index (HBI) for invertebrates—may not fully reflect local conditions. We’ve flagged these cases.
- Data sufficiency is a key consideration: Some watersheds have long-term, robust data. Others may be classified as “Data Deficient” due to many reasons besides lack of data, including monitoring that is incompatible with the FHA, inaccessible data, and the Covid pandemic. Learn more on our data sources page.
For more detail on how each score is calculated, including thresholds, trend analyses, and limitations, please visit our About the Indicators page or consult our Tech Doc for the full methodology.
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Datapoints
This analysis includes all the data we could access—whether from open platforms, agency reports, or historical records. Some datasets were readily available, while others came from hardcopy reports and handwritten notes that we digitized and formatted. We’re grateful to all data providers for sharing their data. Even so, this is only part of the picture. Learn more about data accessibility challenges.
492,396
1,976,715
25,584
157,933
Comparing water quality across sub watersheds
We’ve pulled out a six of the 48 parameters that we display on each Watershed Report so that we can compare. Click through to see all individual water parameter scores.
Very good | Good | Fair | Poor | Very poor | Data deficient | Not scored |
By watershed | Chloride | Dissolved oxygen | Total Phosphorus | Ammonia | Lead | Glyphosate |
|---|---|---|---|---|---|---|
Learn more about our analysis
The overall water quality score is based on how frequently key water quality parameters exceed established guidelines. Individual parameters provide insight into specific concerns, but water quality is complex, and further investigation is encouraged before drawing conclusions about the factors influencing the scores. Here, we’re showing you the percentage of samples within the recommended thresholds over the past five years (2018–2023). These results are compared to the five years preceding (2014–2018) to assess trends. You can visit our glossary page in our Tech Doc for descriptions of each parameter and our Guidelines and Tolerances page to understand the thresholds used in this region.
How's it flowing?
Exploring how flow has changed over time
The Nelson River watershed scored Good.
For some watersheds, there’s been only a minor change, while others have seen shifts including increases and decreases. The Nelson River watershed trend is: Minor increase in flow over time.
We wanted to dive deeper than the score into how flow has changed over time. We took the daily average flow for the Nelson River watershed from the past 30 years (1994-2023) and compared it to the previous 30 years (1964-1993).
Total daily flow
Nelson River watershed’s average daily flow from 1994-2023 compared to 1964-1993. (N=127)
How much has it changed?
The magnitude of change (%) for Nelson River watershed’s total daily flow – 1994-2013 compared to 1964-1993. (N=127))
about our analysis
We used flow data from HYDAT for this watershed, focusing on stations with long-term records—at least 50 years of data and a minimum of 6 months of valid daily flow data per year. This approach ensures inclusion of stations in colder regions, where rivers may freeze part of the year. We then calculated average daily flows across two 30-year periods: 1964–1993 and 1994–2023. By comparing these periods, we smoothed out short-term events like floods or droughts to better understand long-term changes in flow patterns. Learn more about our hydrology calculations in our Tech Doc.
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most common benthic invertebrate taxa observed
Flat-headed mayflies (Heptageniidae)
The score for benthic invertebrates for the Nelson River watershed is Not scored.
Benthic (meaning bottom-dwelling) macroinvertebrates are small aquatic animals and the aquatic larval stages of insects. They include dragonfly and stonefly larvae, snails, worms, and beetles. These creatures make up the backbone of the ecosystem and, since they live there full time, are a great way to understand its health!
This watershed was not scored.
We determined that it would be inappropriate to score some watersheds with the assessment criteria. This included northern regions and some parts of central Canada where they have mud-bottomed rivers.
In northern regions, there are fewer types and quantities of benthic invertebrates because of naturally harsh, cold conditions! The scoring system that works for more Southern areas does not work well in the North because the species found there are naturally tolerant to cold and extreme conditions. In the Central region, mud bottomed rivers in productive landscapes have more tolerant species, too. For both regions, this can lead to misleading scores, making healthy ecosystems appear unhealthy. Therefore, we chose not to score benthic invertebrates in the northern tolerance zones and some central tolerance zones (you’ll see “Not scored”. Learn more in our Tech Doc). We hope to change how we score these regions in the future. We still crunched data, and if we had records, we still spotlighted the most abundant species found there.
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The most frequently reported taxa is the Flat-headed mayflies (Heptageniidae), with 28% of all samples containing them.
About Flat-headed mayflies (Heptageniidae)
Like their name suggests, flat-headed mayflies are best recognized by their characteristically flat heads! They are commonly found in fast-flowing streams on the underside of rocks and logs – their flat heads and bodies help them stay attached and avoid being swept away. They tend to be sensitive to pollution, meaning they indicate healthy waters as they are less commonly observed in contaminated streams.
about our analysis
We assessed benthic macroinvertebrate health using the Hilsenhoff Biotic Index (HBI), which measures how tolerant invertebrate communities are to pollution. We used data from CABIN, the Royal Ontario Museum, Conservation Authorities, and regional programs, focusing on samples identified to at least the family level. For most sub-watersheds, we calculated an average HBI score and assigned a health rating from 1 (very poor) to 5 (very good). However, in some regions—such as the North and certain Prairie rivers—HBI is not considered an appropriate tool due to ecological differences or data limitations. In these cases, we marked the sub-watershed as Not Scored. You can learn more about how we evaluated benthics on our Guidelines and Tolerances page and our Tech Doc.
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Most frequently reported fish:
Brook Stickleback
The fish score for the Nelson River is Good.
Fish, like invertebrates, are an important way to understand water health, since they live in the water full-time.
Here we list out those reported in the past ten years. We also include reported invasive fish species (which are not included in the score calculation, but we thought you’d want to know!).
Here are all the reported fish species for Nelson River watershed during the past 10 years*: brook stickleback, fathead minnow,longnose dace, white sucker, prussian carp (invasive), mountain whitefish, lake chub, rainbow trout, longnose sucker, cutthroat trout
*Because fish sampling is sparse and sampling bias is likely strong, this list is not comprehensive.
Here are the most popular fish across all the sub-watersheds of the Nelson River! Dive into each subwatershed to read all reported fish species for the past 10 years.
By watershed | Most common fish |
|---|---|
Upper South Saskatchewan | Mountain Whitefish |
Bow | Longnose Dace |
Red Deer | Prussian Carp (Invasive) |
Upper North Saskatchewan | Brook Stickleback |
Central North Saskatchewan | Brook Stickleback |
Battle | Fathead Minnow |
Lower North Saskatchewan | Fathead Minnow |
Lower South Saskatchewan | Spottail Shiner |
Qu'Appelle | Brook Stickleback |
Saskatchewan | Spottail Shiner |
Lake Winnipegosis and Lake Manitoba | Yellow Perch |
Assiniboine | Fathead Minnow |
Souris | Fathead Minnow |
Red | Goldeye |
Winnipeg | |
English | |
Eastern Lake Winnipeg | Johnny Darter |
Western Lake Winnipeg | |
Grass and Burntwood | Walleye |
Nelson | White Sucker |
about our analysis
The fish health score is based on trends in native fish species richness, which can reflect overall ecosystem health. Fish monitoring in Canada often relies on presence/absence data, limiting detailed community-level assessments. Still, tracking species richness over time provides valuable insights. In addition to the scores, we present the trend in native species richness over the past ten years (2014–2023) and compare it to the preceding decade (2004–2013) to assess changes. Watersheds are classified into three categories: Good (no significant decline), Fair (a significant decline in either median or total species richness), and Poor (a significant decline in both). Read more in our Tech Doc.
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Dive deeper
Other resources
We recognize that these Reports are a zoomed out way to understand watershed health. You may have additional questions about your local waterbody. We encourage you to find out more about the local conservation work and testing happening in your region. Some regions produce report cards for individual waterbodies, but often this is dependent on resources.
Many regions have opportunities to take action to collect water quality data and get involved in restoration and education opportunities. Learn more about how you might get involved.
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