In 1936, after a biological survey and a consultation of several fish-culturists, it was decided to attempt the introduction of rainbow trout (Salmo gairdnerii) into Clear Lake. This decision was influenced by the urgent need for a suitable game fish in this lake, the chief resort in Riding Mountain Park, and by the wish to check the feasibility of rainbow trout for stocking in lakes of this life zone. Planting, in the years 1937 to 1942 was carried on according to a plan which made use of rearing ponds to increase the size of the fish released. In 1942, when it was found that the rainbow trout were not surviving, it was recommended that planting be discontinued and an attempt made to establish lake trout (Cristivomer namaycush). After three years of planting with adult lake trout it was found that they were surviving in the lake but as yet no evidence of spawning has been obtained. In this report the physical and biological conditions in the lake are described and discussed in relation to the fish-culture experiments. It is concluded that great difficulty will be encountered in attempting to introduce rainbow trout into lakes in which a heavy population of competitor and predator fish is already present.