[2] It has large scales with only 56–70 on its lateral line, fewer gill rakers, all characteristics that indicate a degree of differentiation from the other Prosopium fishes.

[1] The members of this genus are distinguished from the other whitefishes by several characteristics, such as a single flap of skin over the nostril, rather than one; "parr marks" as on trout and char; a round body; and a small toothless mouth.

[5] The genus name Prosopium, meaning "mask" in Greek, refers to the large bones in front of its eyes.

[7] In the Rocky Mountains it is found in cold and rapid streams, and in cool lakes at depths of over 6 metres (20 ft).

[2] In Lake Superior, the amphipod Pontoporeia and various other crustaceans, mostly ostracods, form 77 percent of the pygmy whitefish's diet.