Hydronumerics delivered ecosystem modelling services for Western Port Bay to forecast future changes to water clarity, quality and productivity (in particular seagrass) in response to projections of catchment changes and climate change to 2050. We coupled our bay model to an eWater Source Catchments model developed by Jacobs to quantify the impacts of a range of catchment management scenarios and engineering structures that assisted with a review of the State Environmental Protection Policy for EPA marine water quality and seagrass coverage targets.