Volume 2 In order to conduct oil sands mining operations in the surface mining region of the Athabasca oil sands deposits, most regions require depressurization of the basal sandstone formations. The groundwater produced by depressurization operations is of poor enough quality to be toxic to fish. The purpose of this project is to provide information regarding the acute lethality of oil sands mining and extraction plant wastewaters to fish. Specific objectives were to provide toxicity information on a specific wastewater using Athabasca River water as the diluent and to compare the value of field toxicity studies and the predictive accuracy of laboratory bioassays using treated waters rather than natural waters.