tOyster aquaculture is an expanding industry in the Chesapeake Bay. Oysters remove nitrogen (N) andphosphorus (P) from the water column through filtration and conversion of phytoplankton into shelland tissue, but also continuously excrete these same nutrients back into the water column as inorganiccompounds readily available for plant or algal uptake. The objective of this study was to assess multiplewater quality parameters upstream and downstream of a commercial oyster aquaculture facility in themesohaline region of the Chesapeake Bay. Results of the study indicated a 78.4% average increase intotal ammonia nitrogen (TAN) concentration and a 19.4% decrease in chlorophyll-a (Chl-a) concentrationdownstream of the facility. There was no significant change in the concentration of reactive phosphate(RP), nitrate–nitrogen (NO3−–N), or nitrite–nitrogen (NO2−–N) as water passed through the facility. Itwas determined that velocity of water through the facility had no influence on the change in TAN or Chl-a concentration from upstream to downstream of the facility. Increased reduction in Chl-a concentrationfrom upstream to downstream was related to higher upstream concentrations of Chl-a. There was nocorrelation between increased rates of Chl-a removal and downstream TAN. Results of this study suggestthat oyster aquaculture can significantly increase the amount of available inorganic nitrogen in the watercolumn immediately downstream of a facility, independent of upstream availability of phytoplanktonand flow velocity of water through the facility