In this study the authors have investigated the economic implications for farmers in the area of changes in the availability of irrigation water from the Ashburton River. This report comprises part of a suite of reports commissioned by the Canterbury Regional Council in order to facilitate the drafting of the Ashburton Catchment Management Plan. The implications of changes in water allocation in terms of regional agricultural output and in terms of individual farm productivity, profitability and viability have been examined. An innovative approach to the issue of between season variability has been employed in the survey and analysis.