AbstractPreliminary studies on production by phytoplankton and bacteria in three large mountain lakes in Alberta, Canada (two in Waterton Lakes National Park and one in Jasper National Park) were concluded mainly through the use of the14C technique. The main experiments were conducted in August, 1974, and some were repeated in August, 1975. Net primary production rates varied little from 1974 to 1975, even though there were drastic changes in the phytoplankton composition. Production in the largest lake (max. depth 135 m; mean phytoplankton production 206.5 mgC.m−2.d−1) was approximately twice that for each of the two smaller lakes (max. depths 19 and 27 m: average phytoplankton production 109 mgC.m−2.d−1). Bacterial production estimates averaged 3.8 times those for the phytoplankton production, after a proportionalety large error in the dark‐uptake technique was subtracted. High production rates in the largest lake are probably due to enrichment. Bacterial production rates are comparable to those in smaller oligotrophic lakes