The deepwater cisco was distinguished by usually having fewer than 33 gill rakers, relatively long pectoral fins, and unpigmented jaws.

Its diet consisted of Mysis relicta, fingernail clams, and various aquatic insects.

The main reasons for its extinction was a combination of competition from the invasive alewife,[citation needed] predation by the introduced sea lamprey, and commercial fishing on the Great Lakes.

When a re-evaluation was conducted in several states bordering Lake Michigan in the 1960s, there were no identifiable specimens of the deepwater cisco in any of the samplings.

This served to confirm its extinction,[citation needed] caused by a combination of commercial fishing and invasive predators such as the sea lamprey.