Grass carp (CtenopharynqodonidellaVal.) were introduced to McNeely Lake in August 1985 in an attempt to control nuisance growths of duckweed on the lake surface. Complete control of duckweed was achieved within nine months of the stocking date. No significant changes in nutrient concentrations, dissolved oxygen levels, or general water quality parameters have been observed. Although phytoplankton standing crop, as estimated by chlorophyll a levels remained unchanged, there appears to have been a shift in algal populations toward smaller species and diatoms.