Technical Abstract: Twelve, 0.1-ha earthen ponds at Stoneville, Mississippi were used in a 2-year, double-blind study of the effects of a Bacillus-based bacterial bioaugmentation product on water quality and production of channel catfish Ictalurus punctatus. Each year, six ponds were treated weekly with the microbial product from late May or early June through October, and six ponds were designated as untreated controls. Mean concentrations of chlorophyll a, nitrite-N, and total ammonia-N did not significantly differ (P > 0.05) between bacteria-treated and untreated ponds in the first year; however, in the second year, mean chlorophyll-a concentrations were higher (P < 0.05) and nitrite-N and total ammonia-N concentrations were lower (P < 0.05) in bacteria-treated ponds than in untreated ponds. Reductions in dissolved inorganic nitrogen concentrations were more likely due to increased phytoplankton growth (i.e., increased algal assimilation) than to a direct effect of bacterial inoculation. The mechanism by which bioaugmentation may have enhanced phytoplankton growth is unknown and contradicts several past studies. Net fish production and feed conversion ratios were not affected by bacterial treatment in either year (P > 0.05); accordingly, there is no economic incentive to use Bacillus bacterial bioaugmentation products in channel catfish ponds.