A study was conducted in Lake Benbrook and Squaw Creek reservoirs, Texas, to determine whether naturally occurring phytoplankton and crustacean zooplankton abundance in selected coves could be increased by fertilization. In each reservoir, I cove was fertilized once a week for 4 weeks using inorganic fertilizer (liquid 10-34-0, N-P- K, applied at I mg/liter PP,), 1 cove was fertilized with the same inorganic fertilizer plus organic fertilizer (cottonseed meal applied at 225 kg/ ha), and I cove received no fertilizer as a control. Nutrient and plankton levels in the coves were monitored before, during, and after fertilizer application. Nutrient levels increased imediately after application of fertilizer, but returned to pre-treatment levels within I week. Fertilized coves did not have higher phytoplankton or zooplankton densities than non-fertilized coves. Dilution resulting from high water exchange rates between coves and the main reservoir was suspected as the cause for lack of fertilization effects.