The purpose of the report was to discover, describe, and if possible, quantify the relationships between blue-green algae and the fishes of Upper Klamath Lake. Recognition of these relationships should have predictive value in dealing with similar shallow bodies of water, or with impoundments which might receive water from Upper Klamath Lake. Attention was given to direct effects through a program of sampling the fish population, and to indirect influences through study of the benthic community upon which the fish depend for food. Aspects of the limnology basic to the objective were investigated.