Lake Diefenbaker (LD) is a large reservoir on the South Saskatchewan River used for agricultural irrigation, drinking water, and recreation. Our objectives were to determine the distribution and abundance of bacterial indicators in embayments and the main channel of LD and to relate these to environmental factors. Total coliforms (TCs), fecal coliforms (FCs), and fecal indicator bacteria (i.e., Escherichia coli) were measured concurrently with water quality parameters. Although TCs, FCs, and E. coli were present in LD, they rarely exceeded the TC and FC Canadian Council of Ministers of the Environment (CCME) water quality standards for agricultural use (1000 colony-forming units (CFU) per 100 mL and 100 CFU per 100 mL, respectively). The correlation between the bacterial indicators in the sediments and the water column indicates that higher embayment abundances may be related to sediment loading and (or) resuspension events in these frequently mixed embayments. With higher water temperatures and water levels, as well as higher microbial activity, CCME bacterial limits may be exceeded. The greatest contributor to bacterial indicator abundance was water temperature. We predict that water quality standards will be exceeded more frequently with climate warming.