This paper reports on an analysis of irrigator water demand and profit changes across varying annual water availability, crop water requirements, and river salinity conditions for irrigation along the South Australian portion of the Lower Murray. The paper also investigates the validity of the current relationship between salinity of irrigation water and irrigated crop yield underlying MDBC salinity offset investments. The assumption implicit in the current MDBC net benefits formula may be mis-specified in that the possibility to avoid yield loss with additional leaching is not accounted for. This paper reports how that mis-specification, that irrigators would simply accept yield losses, leads to overstatement of the benefits of actions to decrease salinity.