Dr Paul Humphries is a professor at Charles Sturt University and based at Albury/Wodonga. His interests mostly relate to rivers and their ecology.

Most of his work over the last 20 years has focused on the relationship between riverine biota and flow.

While Dr Humphries couldn’t comment directly on the health of Lake Cathie’s water system, he anecdotally gave his expert opinion based on previous research.

Last week Lake Cathie hit the required factors to be artificially opened to the ocean by Port Macquarie-Hastings Council.

“The current water level is 0.05m AHD and salinity is between 40 and 42 ppt, therefore a lake opening trigger has been reached,” council director Melissa Watkins said.

However the lake will not be opened by council due to several risks associated with the action.

Ms Watkins said the risks include low lake water levels which limit the success of an excavated channel remaining open, the likelihood of excessive sand build up in the recently dredged area and potential risk for red weed to enter and become stuck in the lake should it naturally close quickly.

Ms Watkins said another risk is the likelihood of insufficient flushing of the lake and system shock when very cold ocean water meets warm lake water.

However Dr Humphries said most animals can cope with big changes in temperature, as long as the change is introduced slowly.

“If the change occurs over 24 hours they will be fine,” he said.

In response to the smell that residents have been noticing at the location, Dr Humphries said it could be caused by a number of factors.

“Rich nutrients in the water can stimulate the growth of algae which can decompose and settle at the bottom of the water,” he said.

“That material can rot and release hydrogen sulphide and this can create a rotten egg gas smell."

Dr Humphries said if the water level of a lake or estuary is low it can cause hypersalinity and kill fish and invertebrates, if they are not adapted to those conditions.

“It can be up to 10 times as salty as the ocean,” he said.

“This can cause many invertebrates to die.”

Dr Humphries said he has witnessed artificial opening at estuaries where the water quality is improved when there is a mix of water types.

He referred to the Dawesville Channel, south of Mandurah in Western Australia which was created to alleviate an environmental problem which had developed where the deep estuarine system had become eutrophic.