Investigations of photosynthesis were conducted upon a small polluted river, the Passaic River in New Jersey, including effects upon the general oxygen regimen of the river. Data obtained showed variation of photosynthetic oxygen with water depth, time of day, and with the seasons. Attempts were made to develop a method of mathematically modelling net photosynthesis effect based on water quality and environmental characteristics; but results were not sufficiently satisfactory to be definitive. A comparison of oxygenation effects due to photosynthesis and the natural atmospheric reaeration, respectively, showed that photosynthesis contributed about 20% of the total oxygen added; the proportion being independent of the stream discharge. Moreover, if the dissolved oxygen concentration of the river were at a higher level, this proportion would rise. Nutrient levels in the water were high, the phosphate levels in particular were many times that necessary to maintain algae growth. (Author)