The rates of algal production and Sphaerotilus assimilation in the lower Logan River benthos were investigated in 1966 and 1967 . The rate of annual gross primary production (3,416 Kcal/m2/yr) was estimated from the relation of pigments to the photosynthetic rate of benthic communities in a submersible, metabolism chamber. The photosybthetic rate was predicted with high precision when a measure of the accessory pigments (D480/D665 and/or chlorophyll-c ) was considered with the chlorophyll-a . The pigment density estimates were obtained from the community present on paraffin-coated, concrete hemispheres after immersion in the river for periods ranging from 11 to 20 weeks. The daily rate of energy utilization by Sphaerotilus (1.3 c a l/m2/day) was estimated from the observed generation time of this bacterium on glass slides suspended in the river at various locations and metabolic coefficients obtained from other sources. The magnitude of microbial activity in the river water Has estimated to be 448 cal/m2/day. The accumulation rate of Sphaerotilus biomas s on glass slides was 0.3 mg? (net weight)/m-/48 hours , and could be predicted from the temperature, nitrate (plus nitrate) content , and the dissolved organic carbon content of the river water. The generation time of Sphaerotilus (average was 20 hours) could be predicted f rom temperature, nitrate (plus nitrite) content, and velocity of t he water. The daily P/B coefficient for this bacterium was 1.20.