A literature review and evaluation of methods used to determine rates of bacterial uptake (heterotrophic assimilation) of organic substrates in fresh water systems was undertaken. The uptake of a "universal" substrate - radiolabelled glutamic acid - was determined in order to assess the effects of organic compounds from both natural (oil sands) and industrial (oil extraction and refining) sources on the rate of heterotrophic assimilation in the Athabasca River. Only partial results are available due to an unanticipated termination of this project for reasons beyond our control. On the basis of this preliminary investigation, it was concluded that oil sands mining wastes have no significant stimulatory or toxic effect on the uptake of glutamic acid by the planktonic bacterial populations of the Athabasca River.