The aquatic macrophytes Elodea canadensis and Potamogeton crispus, Callitriche sp.; and the algae Cladophora sp., Nitella flexilis, Oscillatoria sp., and Microspora sp. were tested for their ammonium nitrogen absorption rate, alkaline phosphatase enzyme activity, extractable surplus phosphorus content, and nitrogen and phosphorus tissue content. Comparisons of the nutritional level of the test species were made with corresponding levels of nitrogen and phosphorus monitored in streamwater, adsorbed on stream sediments, and in the interstitial water of the sediments. Corresponding laboratory cultures were maintained with media sufficient or depleted in nutrients. Study sites selected included stream segments receiving both natural and man derived inputs of nutrients and included levels of phosphorus ranging from low baseline concentrations to high levels imparted by discharges from secondary sewage treatment plant effluents.