A method for monitoring net and gross community oxygen productivity, community respiration, photosynthetic efficiency, and reaeration coefficient has been tested in five contrasting rivers. The technique uses relatively inexpensive digital data collection and processing, and allows detection of incipient eutrophication due to nutrient input and excess oxygen demand from organic waste input. Oxygen concentration, temperature, and solar radiation are recorded over a 24-h period and are the data used to calculate the parameters necessary for water quality monitoring. A few weeks data, taken during summer low-flow conditions, are then used to discriminate water quality.