This study provides a method to combine hydro-ecological response model outputs and nonmarket economic values of wetland inundation to estimate a unit price of environmental water. We show how an integrated socio-economic and hydro-ecological modelling approach may assist policy makers with water allocation decisions across competing uses. The IBIS decision support system incorporates a hydro-ecological model and is used to estimate the habitat suitability condition of wetland attributes for a given hydrology scenario. Non-use economic values of wetland attributes obtained by non-market valuation studies are then linked to the hydro-ecological model outputs to estimate marginal value of environmental flows. The contribution is to provide a robust, scientifically and economically valid method to estimate the marginal value of environmental water and to quantitatively evaluate the trade-offs involved in water allocation decisions across competing uses for water.