Abstract
The limits to water availability are set, not only by the quantity of water in storages or streams but, more fundamentally, by acceptable levels of environmental health. An interpretation of water quality as inclusive of biological quality infers that environmental health and water quality are interdependent. Consequently, to make effective judgements of water availability managers of water resources need information that presents environmental condition in its regional context. This paper presents the results of research that explores the use of stream turbidity as an indicator of environmental condition, identifies a regional statistical model, and constructs a method to display the distribution of model predictions over a large region of south‐eastern Australia. The practical advantage of this approach is that it provides managers with the ability to identify sites that differ significantly from modelled water quality and flag them for further investigation. The major project outputs are a map of regional catchments showing standardised residuals and a raster representation of the state of Victoria in which cell values indicate predicted stream turbidity. Important to this project was the novel use of Geographic Information System technology to process national and regional scale digital data sets using tools developed for catchment scale hydrological models.