During studies of the environmental effects of oil sands development in northeastern Alberta in 1976–1977, 36 species of Ephemeroptera and 21 of Plecoptera were collected using various techniques. Individuals of 18 mayflies and 17 stoneflies were taken in numbers sufficient to determine their basic life histories and habitat preferences. Among the mayflies, 8 (possibly 10) species exhibited fast seasonal development, 8 slow seasonal, and 2 non‐seasonal. Among the Plecoptera, these patterns were exhibited by 5, 7 and 5 species, respectively. Nymphs of most fast seasonal mayflies developed in pools and silty backwaters, often in association with aquatic macrophytes. Slow seasonal mayflies and most stoneflies were found in riffles, or on bedrock and debris in the Athabasca River. The fauna included a mixture of Eastern, northern and cordilleran species. Eastern species probably reached the Athabasca River drainage via glacial Lake Agassiz.