The West Interceptor Ditch was constructed to divert water from several small creeks into Bridge Creek, a tributary of Beaver Creek, which eventually flows into the Athabasca River. During the diversion process, a portion of lower Beaver Creek was restructured to accommodate discharge from the North Starter Dyke. The present study, initiated in May, 1977, and completed in September, 1977, is mainly concerned with this restructured section. Specifically, the objectives of the study were to: 1) describe existing environmental conditions in, and to document natural biological colonization of, the West Interceptor Ditch, and 2) determine the degree of biological colonization of the recently altered section in lower Beaver Creek.