The Pesticide Chemicals Branch of Alberta Environment conducted a monitoring program in 1981 related to two methoxychlor treatments of the Athabasca River for black fly (Diptera: Simulium arcticum) control. Three populations of black fly larvae were observed in 1981 and the first two populations were reduced by 95.4% (May 20/21 treatment) and 96.5% (June 19 treatment) respectively. Population reductions of non-target organisms due to methoxychlor was limited for the May 20/21 treatment but was considerable for the June 19 treatment. Water samples collected from the Athabasca River at Fort McMurray contained only trace amounts of methoxychlor. Adult black fly activity in the farming area peaked in late July, correlating with expected adult emergence.