Keller Lake, with an area of 413 km2, is an essentially unexploited lake in the Northwest Territories. Results of an experimental fishery and a commercial fishery of short duration are described. Effects of gillnet selection are discussed for the two major species, lake trout and humpback whitefish, and it is concluded that the sample obtained represents the actual population, at least for sizes over 350 mm in length. There were very few fish in the 350–500 mm size range, or in age-groups 9–13; but size and age were not closely correlated. The population structure is likened to a forest climax condition. A mechanism for the dynamics of the system is proposed, which can be tested. Size distribution of the population is considered to be in the form of a standing wave with the shape of a normal distribution for the main body of the population; age structure changes with time but will retain a bimodal condition continuously. The effect of cropping on a population structure of this type is discussed.