The bottom fauna of the deep water of Cultus Lake averages about 530 grams per square meter, dry weight, during the period January-May, and 720 in June-September. This is divided almost equally between Chironomidae and Oligochaeta, other organisms being negligible. The midges are extensively used as food by trout and other fishes during their season of emergence in winter and spring. The spatial distribution of the organisms is usually close to random as between samples 500 square centimeters in area, the only exception being that the oligochaetes were strongly bunched in winter.