Various stream processes which contribute to reoxygenation or deoxygenation were studied separately under controlled conditions in aquaria and in a research flume. Stream processes were simulated as a model river consisting of benthos and photosynthetic organisms. In another channel an identical ecosystem was established and stressed with an organic pollutant. The conditions established in these model rivers were those assumed in the development of various sag equations. The stressed ecosystem behaved in accordance with sag equations proving the validity of the classical predictive formulas and validity of simulation of stream processes in the model river. A formulation for atmospheric reaeration constants for flowing systems as a function of velocity and depth was developed from data obtained in the model river. (Author)