Average estuary depths below 0.6 m AHD have been calculated by dividing estuary volume by surface area excluding saltmarsh, which is generally found only above mean high water level.; ; Average estuary depths were calculated for a number of purposes:; * exploratory analysis of empirical relationships for predicting water volume in those estuaries without hydrosurveys; * checking the validity of assumptions made in deriving estuary surface areas and volumes; * as a variable in the development of a classification system.; ; 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.