Syncrude Canada Ltd. is producing synthetic crude oil from a surface mine on the eastern portion of Crown Lease 17, Alberta. Aquatic Environments Limited was commissioned to survey the MacKay River which crosses Leases 17 and 22, also held by Syncrude. The survey is intended to provide a baseline, as Syncrude's present operations do not affect the MacKay watershed. The pattern of discharge in the MacKay River in 1977 was characterized by three peaks, two major (April 19 and July 8) and one minor (October 16). Peak discharge for the year was 22.5 m3/sec and the low 0.2 m3/sec. Mean discharge was 4.2 m3/sec per day and total discharge was 176.6 x 106 m3. The densities of periphyton were highest on natural substrates than on either artificial substrate. In general, the densities were low throughout the summer but increased in September. At some locations, however, densities on glass substrates were highest in July. A total of 80 benthic macroinvertebrate taxa was collected, with 59 taxa found at the Upper Station, 56 at the Middle Station, and 49 at the Lower Station. In total, 19 fish species were collected from the MacKay River. The common or abundant species are: goldeye, northern pike, lake chub, longnose dace, longnose sucker, white sucker, trout-perch, walleye, and slimy sculpin.