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 Unfortunately the information available on numbers of waterfowl using the area is outdated, but there is no reason to suppose that the lake is still not exceedingly important.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.
BirdLife International (2020) Important Bird Areas factsheet: Mills Lake. Downloaded from http://www.birdlife.org on 09/07/2020.