Information on the spatial and temporal characteristics of ambient dissolved oxygen in the southwestern New Brunswick area of the Bay of Fundy is presented to help develop an understanding of dynamics of oxygen and salmon cage culture in the region. Some modelling efforts focussed on dissolved oxygen issues associated with fish farming in the area are also presented. A description and application of a simple oxygen depletion index is proposed to help identify the influence of salmon cage culture on the regional and farm-scale dissolved oxygen concentrations. The chapter concludes with a brief summary and discussion of observations and model development required to enhance the understanding of oxygen dynamics in the farms and bays of southwestern New Brunswick. The knowledge can be used by industry in their farm management practices and by environmental regulators in their efforts to define and sustain water quality standards.