Three species of aquatic macrophytes from an agricultural drainage ditch were analyzed for N, P, and organic C throughout the 1976 growing season. These macrophytes accumulated large amounts of these nutrients, averaging 26.49 mg N g-1 dry weight, 5.89 mg P g-1 dry weight and 353.7 mg C g-1 dry weight. Measured breakdown rates of Potamogeton nodosus Poir. were 0.0312 d-1 and 0.0408 d-1 at two different sites. C:N of the decaying macrophytes was less than 17:1 throughout the study. Analyses of covariance of the nutrient accumulation and breakdown of aquatic macrophytes revealed no differences among species or sites.