On three occasions during the period May-October, 1978, R.L.& L. Environmental Services Ltd. conducted fish sampling in the Beaver Creek Diversion System. These efforts were oriented towards providing an inventory of postdiversion fish populations. The study was designed not only to update the existing data base, but to provide quantified and reproducible catch/unit effort data (CUE) which could effectively serve as a basis for future monitoring of fish populations. Sampling gear employed in the study included gill nets, beach seine, and back-pack electrofisher. While a total of 11 species were encountered in the study area, only 6 were recorded in the upper diversion system (i.e., upstream of the Poplar Creek dam). Included in this latter group were two species of catostomids (white sucker, longnose sucker), the fathead minnow, brook stickleback, lake chub and spoonhead sculpin (Upper Beaver Creek only). Species collected in Poplar Creek, additional to those recorded in the upper diversion system, were Arctic grayling, northern pike, yellow perch, burbot and troutperch. The spoonhead sculpin was not collected in Poplar Creek. Pertinent life history information was collected for each of the species in the study area and subsequently analysed by computer. This material is provided in a separate data volume. Because of the significance of the white sucker in the diversion system, life history data for this species are presented in this report.