A total of 82 estuaries in NSW have hydrographic surveys of their bathymetry. Surveys have been conducted over the last 100 years or so with many over the last 30 years in paper format and, since 1992, in digital xyz format. Of the 82 surveys, 49 were suitable for gridding into a Digital Elevation Model with a horizontal resolution of generally 12.5 m on a uniform or strained grid. Topography was available on a 25 m regular grid over NSW and was merged with bathymetry to create a continuous surface. Estuary water volumes at 0.6 m AHD were calculated for 49 estuaries from the gridded bathymetry. Empirical relationships between estuary surface area and estuary volume at 0.6 m AHD were developed for each geomorphic type and applied to the remaining 131 estuaries to give estimates of volumes for all estuaries in NSW.; ; Estuary water volumes were estimated to support the development of a new response-based estuary classification system based on dilution and flushing characteristics. The classification system was used to stratify estuaries in NSW for the development of reference conditions and the design of a sampling program of chlorophyll a, turbidity and associated water quality parameters to assess estuary health.