The Hunter River drains the largest coastal catchment in New South Wales, covering some 22,000 square kilometres.
The Hunter region supports a range of agricultural activities including wineries, dairying, vegetables, fodder, beef and horse breeding.
Also located in the valley are over 20 of the world's largest coal mines and three power stations, including Australia's largest electricity generator.
Salt occurs naturally in many of the rocks and soils of the Hunter Valley. Some of this salt is leached into groundwater and nearby rivers.
Human activities also have an impact on the saltiness of the river. During coal mining, salty water collects in mine pits and shafts and has to be pumped out to allow mining operations to continue.
Electricity generation uses large volumes of river water for cooling. As this water evaporates, natural salt is concentrated in the water that remains.
Hunter River Catchment
Water salinity is estimated by measuring electrical conductivity. The saltier the water, the more electricity it can conduct. Electrical conductivity is measured in microsiemens per centimetre (µS/cm). Drinking quality water usually measures between 600 and 1200 µS/cm.