Water hyacinth, Eichhornia crassipes, growth and nutrient uptake rates, as influenced by different N sources and N transformations, were measured using microcosm aquaculture systems. Net productivity was highest in the system receiving equal amounts of NH4+ and NO3- (at 10 mg N 1-1 each) and decreased in the order of NO3-, NH4+, urea (added at 20 mg N 1-1 each), and methane digestor effluent (at 6 mg N 1-1). During the first 7-wk study (average ambient air temperature was 26-28?C), biomass yields were in the range of 19-53 g dry wt m-2 day-', while between the 8th and 12th wk (average ambient air temperature was 16-22?C), biomass yields were in the range of 10-33 g dry wt m-2 day-1. In the systems with either NH4+ or NO3-, or both added in equal proportions, about 14-20% of the total yield was contributed by roots, whereas in the system with urea and digestor effluent, roots contributed about 23 and 44% of the total yield, respectively. Nitrogen and P uptake per unit area followed trends similar to biomass yields. Nitrogen uptake rates were in the range of 533-2,161 mg N m-2 day-1 for the systems receiving NH4+, NO3-, and urea, while uptake rates were in the range of 124-602 mg N m -2 day -1for the system receiving methane digestor effluent. Phosphorus uptake rates were found to be in the range of 59542 mg P m2 day-'. Under the most favorable conditions, maximum recorded biomass yield was 53 g dry wt m-2 day-1, with N and P removal rate of 2,161 mg N m-2 day-1 and 542 mg P m-2 day-1, indicating the potential of water hyacinth to produce large amounts of biomass which can be potentially used as afeedstock to produce methane.