Like most minnows, the lake chub is a small fish, rarely attaining a length of more than six inches. Adults are dark brown to green above and pale below, with a dusky lateral stripe that varies from a very distinct marking to an inconspicuous line. Breeding males develop tubercles on the head and the pectoral fin. In addition to the development of tubercles, males also display reddish-orange spots at the base of the pectoral fin and just behind the gill cover. Lake chubs have large eyes and a rounded barbel situated on but not quite at the end of the upper jaw.
Lake chubs are mostly carnivorous, feeding on aquatic insects and small crustaceans.
In lakes and streams with few other small minnow species, lake chubs are an important link in the food web. By feeding on small organisms that are not available to larger fish and fish-eating birds and mammals, lake chubs channel food energy to these larger animals in many northern lakes and streams. Possibly, the species was once more common and widespread during the cooler glacial periods of the Pleistocene. As the climate changed, lake chubs could no longer survive in the warmer prairie streams and rivers but were able to thrive in cool Black Hills streams. Another intriguing possibility involves a geological process known as stream capture.