Mills Lake is formed by a widening of the upper Mackenzie River, and is found at a point where the Horn River joins the Mackenzie River. It is a circular lake, about 20 km wide that lies downstream from Fort Providence, Northwest Territories. The lake holds extensive marshes and other vegetation communities, such as floating sedge mats, and other emergent and submergent aquatic vegetation. The surrounding shorelines are low-lying and often sandy.
The marsh and sedge shallow-water zones of Mills Lake attract thousands of migrating waterfowl during fall migration in September and October. The northern and eastern shoreline, and delta areas are most favoured. Unfortunately the information available on numbers of waterfowl using the area is outdated, but there is no reason to suppose that the lake is still not exceedingly important. The numbers available from 1972 show that peak numbers on one day were: 9,860 Greater White-fronted Geese, 2,190 Tundra Swans, nearly 4,000 Snow Geese, 1,390 Canada Geese (Short-Grass Prairie population) and an impressive 27,000 ducks. These ducks were primarily American Wigeon, Northern Pintail, Mallard and Canvasback. Additionally, in some years a few thousand American Coots can be observed feeding on the Potamogeton plants growing in the lake. Several of the geese species have increased in number over the last decade and so it is unclear what percentage of the current populations uses the area. Using 1990s estimates, the numbers above represent over 1% of the mid-continent Greater White-fronted Goose population, and over 1% of the North American population of Tundra Swan. Estimates from the 1970s show that 2% of the Western Central Flyway population of Snow Geese passed through Mills Lake.
Lesser Snow Goose (white phase) (Western Central Flyway (NW Can/AK))
Note: species shown in bold indicate that their population level (as estimated by the maximum number) exceeds at least one of the IBA thresholds (national, continental or global). The site may still not qualify for that level of IBA if the maximum number reflects an exceptional or historical occurence.
There are no known threats to the habitats of Mills Lake. Nonetheless, there is the possibility that river dredging (for barge traffic) could disturb birds if it were done in September. Also, there have been proposals to dam the Slave River, which if done, could affect water flow to the Mackenzie. Finally, haying and grazing, if increased in the area, would change the marsh communities.
The importance of Mills Lake has been recognized before by both the International Biological Programme, and Canadian Wildlife Service as a Key Migratory Bird Terrestrial Habitat Site.
The IBA Program is an international conservation initiative coordinated by BirdLife
International. The Canadian co-partners for the IBA Program are Bird Studies Canada and Nature Canada.