The thermal effects of the Brandon Generating Station on the Assiniboine River were investigated from October 23, 1973 to August 9, 1974. Physical, chemical and biological sampling and analysis were performed throughout the study period. The biological sampling performed revealed development of macro-invertebrates during late February and early March, when the organisms are normally in a dormant state. The reach of the Assiniboine affected by the thermal discharge was repopulated with macro-invertebrates by July. The physical and chemical data did not reveal any detrimental effects on the Assiniboine River for the flow conditions of the river and the degree of generating station operation experiences during the study period.