Phosphorus was partitioned among the major structures of Potamogeton crispus (roots, turions, leaves and stems) at regular intervals during May and June of 1988 to determine the pathway of phosphorus in the plant matter during growth and die back of the population. Phosphorus concentration in the plants declined from an average of 0.25% of dry weight to 0.13% of dry weight during the period in which biomass doubled and so the total mass of phosphorus in the P. crispus population was essentially unchanged. There was no evidence that phosphorus was translocated from stem and leaf tissue to turions and roots during senescence. The development of turions by P. crispus and the hypothesized conservation of phosphorus in these reproductive tissues does not explain the lower than expected pulse of phosphorus in the water column coincident with the decomposition of these aquatic plants.