South Twin Lake is a relatively shallow, medium-sized lake located within the White Earth Indian Reservation and is part of the larger Wild Rice River watershed. The lakeshore is fairly developed along the south, southwestern, and northern shores. South Twin’s watershed is small relative to its surface area (6:1 ratio) and land use is dominated by forested, wetland, and water land use types.
Aquatic plants communities in South Twin are moderately diverse with a high prevalence of Chara, which is an important species for juvenile and non-game fish and maintaining high water clarity. These communities are fairly patchy throughout the lake, with the densest patches occurring along the shorelines with the highest amount of development.
The fish community of South Twin Lake is diverse with substantial populations of cold-, cool-, and warm-water species and several sensitive non-game species that are intolerant to disturbance. Currently, South Twin is managed primarily for Walleye and Northern Pike and the Walleye population is supplemented through biennial fingerling stocking. Past surveys show that Northern Pike abundance appears to be trending upward, while size may be trending downward. Yellow Perch, an important cool-water forage fish, have declined in recent years; however, recruitment of this species has varied widely during the past two decades. Cisco are present in South Twin and are an important cold-water forage fish. Cisco habitat is marginal because the lake is relatively shallow with little cold-water refuge during summer. Consequently, Cisco populations in South Twin may be threatened by warmer water temperatures brought on by climate change. Nevertheless, for reasons uncertain, Cisco numbers in South Twin have bucked a statewide trend of declining populations and have actually increased over time.
South Twin Lake was selected as a Sentinel Lake to represent a cold-water, mesotrophic lake in the Northern Lakes and Forests ecoregion.