The Athabasca rainbow trout refers to a complex of populations that are native to Alberta waters and are confined to the upper Athabasca River and its tributaries including the McLeod, Berland/Wildhay, and Freeman revers and their headwater streams. The biology of the native Athabasca rainbow trout differs from that of introduced rainbow trout, which are abundant in southern Alberta, in that the native trout spawn later in the spring, grow much more slowly, and mature at a smaller size than their introduced counterparts. The native rainbow trout appear to be better adapted to cold, unproductive headwater environments than introduced varieties.