You will need to be part of the Hunter River Salinity Trading Scheme in order to discharge salt water into the Hunter River catchment.
The scheme provides a number of salt credits that allow holders to discharge into the river catchment. The number of credits you hold will determine the amount of water you can discharge. You can buy from the regulator or trade salt credits with other scheme participants.
Salt water can only be discharged when the river is in high or flood flow.
You will need to hold the appropriate environmental licence to participate in the scheme.