Studies of algal nutrient interchange between sediment and water under environmental conditions were carried out in Upper Klamath Lake, Oregon. Experimental 'pools' of lake water in contact with the sediment and experimental pools of water not exposed to the sediment were compared with the open lake. Water quality measurements were made to determine whether interchange processes could be observed directly in the water, to establish conditions for laboratory interchange tests, and to compare lake conditions with the experimental pools. Interchange definitely occurred when Oscillatora floated to the lake surface with attached sediment which contained soluble nitrogen and phosphorus compounds. The effects of gas evolution, wind, currents, fish, boating, benthos, diffusion, etc., on the shallow lakes was not quantitatively determined, but it seems quite probable that anything that stirs the sediment causes interchange of nutrients. (Author)