Narragansett Bay, the largest estuary in the northeastern U.S., is a heavily urbanized watershed impacted by deposition and runoff. Nutrient budgets and local policy rely on deposition data from a 1990 study that did not include any direct observations of dry deposition of gaseous ammonia (NH3) and particulate ammonium (NH4+) due to uncertainties in their flux direction and measurement difficulty. Recent precipitation measurements show that wet deposition of NH4+ to the Bay has increased by a factor of 6 over the past three decades, leading to a 2.5-fold increase in wet nitrogen (N) deposition. The documented increase in wet deposition of NH4+ concurrent with managed nutrient reductions in urbanized estuaries has potentially increased the impacts of atmospheric N deposition, including the dry deposition of NH3 and NH4+. However, a scarcity of measurements hinders our interpretation of this important N source. For the first time over Narragansett Bay, and to our knowledge over open water, dry (particulate and gas phase) deposition of total NHx (NHx = NH3 + NH4+) and bidirectional NH3 flux was quantified using a relaxed eddy accumulation sampling technique. We find that total N entering the Bay from the atmosphere has doubled since 1990. Dry deposition of NHx comprises 9.6% of total N deposition. During the fall season, the dominant flux direction for NH3 is upward, which also has implications for urban air quality. We estimate that NH3 emitted from the Bay to the atmosphere makes up to 10% of the local NH3 emission budget.