The direct epifluorescence method has been adapted for counting bacteria in the sometimes turbid water of the Athabasca River and this method has been used to quantify planktonic bacteria. Monthly samples over an annual cycle beginning in May 1976 showed this population ranged from 1 x 105 to 2 x 106 cells per millilitre. A statistical analysis of site-to-site variations and averages of bacterial numbers from sites upstream and downstream from Fort McMurray and the GCOS plant site have shown there is no discernible effect on the bacterial populations by either facility. Further, there is a definite site-to-site variation in the bacterial numbers as well as seasonal variations at each site. The direct microscopic examination, including scanning electron microscopy, has shown that the planktonic bacteria are generally free-floating with some colonization of organic detrital materials. Silt particles are generally free of bacteria. The statistical analysis of the ATP measurement showed that this method for estimation of bacterial biomass could not be used in the Athabasca. When bacterial enumeration data were compared to flow, total organic carbon, nitrogen (Kjeldahl), and conductivity, there was no correlation. However there was a slight negative correlation of bacterial numbers with turbidity and total unfilterable residue.