A fifteen month pollution survey of the Sacramento River showed the effects of agricultural, municipal and industrial discharges into the river. Limitations in both classical and modern approaches to describing oxygen supplies and demands are evidenced by such factors as (1) frequent nighttime increases in oxygen concentrations, (2) derivation of negative values for reaeration coefficients in the Streeter-Phelps formula, and (3) diurnal variations in oxygen levels which preclude application of Odum’s diurnal curve analysis. Each of these can be explained on the basis of changes in rates of respiration or BOD satisfaction. Quantitative descriptions and predictions require a much more complete knowledge of respiration rates of aquatic communities of both natural and disturbed conditions than is presently available.