During 1977, the second year of a two-year study, the fish populations of the Athabasca Rive: were investigated in two general areas downstream of Fort McMurray. Field work was carried out from mid-April to early November in the Mildred Lake study area and from mid-May to mid-October in the Delta study area. Fish were collected with gill nets, seines, and angling gear in order to identify the species present and their distribution and relative abundance during the open-water period, and to obtain samples for life history analysis. A conventional tagging program was undertaken to delineate migration patterns for the major fish species. The 1977 study identified 24 fish species from the lower Athabasca River, 11 of which were common. All 24 species were present in samples from the Mildred Lake study area, while only 18 were captured in the Delta study area. A total of 27 species were identified from the Athabasca River during the two years of the study. Major upstream movements of walleye, goldeye, longnose sucker, and white sucker occurred in the Athabasca River during early spring. These runs were apparently initiated under ice-cover and reached the Mildred Lake study area before the ice had left the Athabasca River. The walleye and sucker runs were spawning migrations and the early spring upstream movements of these species were followed by a more gradual downstream dispersal that continued throughout the summer. The entire lower Athabasca River is important as a summer feeding area for immature goldeye which enter the study area prior to breakup and departed in late autumn. These goldeye are thought to belong to the population that spawns in the Peace-Athabasca Delta. Thus, the lower Athabasca River may play a major role in the maintenance of that population. A large upstream spawning migration of lake whitefish occurred during September and October. Some whitefish returned to Lake Athabasca shortly after spawning but others may have overwintered in the Athabasca River. Trout-perch, flathead chub, emerald shiner, and lake chub were the major forage fishes observed.