Camden Haven High School field trip reveals critically high saline levels in Lake Cathie and Lake Innes

A dead fish found on the shores of Lake Innes, near Port Macquarie.

A dead fish found on the shores of Lake Innes, near Port Macquarie.

A SCHOOL excursion into the waterways at Lake Cathie and Lake Innes have uncovered disturbing results with high salinity levels and dead fish painting a dire picture of a starving marine environment.

Camden Haven High School students joined local environmental scientist and marine biologist Dr Deb Geronimi on the trek on May 31.

The team ventured nine kilometres into the waterway and were shocked by what they found at Lake Innes near Port Macquarie with test results confirming the ecology of both lakes is in crisis.

Students collected water samples from the surface of five locations around Lake Cathie. They tested the salinity, pH, nitrites and ammonia with some alarming results.

"Salinity was 60 parts per thousand (ppt) and there were dead and dying fish everywhere including adult stripped scads and longtoms measuring up to a metre long," Dr Geronimi said.

"These fish species are extremely hardy but they cannot tolerate these kinds of salinity levels.

"Also, dead pipis, crabs and yabbies were scattered on the shore. Ammonia was also detected in the water at Lake Innes, which is indicative of decomposing organisms."

Camden Haven High students conduct water testing in Lake Cathie and Lake Innes.

Camden Haven High students conduct water testing in Lake Cathie and Lake Innes.

At the Perch Hole near Lake Cathie, salinity was 50ppt while Lake Innes measured 60ppt. Normal ocean seawater has a salinity of 35ppt

At the Kenwood Drive bridge at Lake Cathie, testing found pH levels were well above 8.8 making it almost unsustainable for marine life to survive.

"The ecology is crashing," Dr Geronimi said.

"When Lake Cathie is open to the ocean, it's beautiful and it has continuous seawater flushing twice a day.

"The health of the lake begins with the very smallest micro-organisms. They were the first living organisms on this planet and will probably be the last.

"These micro-organisms are struggling to adapt to the constantly changing environment of the lake, and as a result the nutrients are not being recycled, decomposition is slowing and the nitrogen cycle is unbalanced.

"My suggestion would be to keep (the lake) open all the time and fill Lake Innes back in allowing it to restore to a freshwater lake."

Critical situation: Travis Fredericks inspects the depleted Lake Cathie. Photo: Lisa Willows

Critical situation: Travis Fredericks inspects the depleted Lake Cathie. Photo: Lisa Willows

Since the 1960s council has artificially opened Lake Cathie to the ocean by excavating a channel once the water has reached a trigger level during heavy rain.

Lake Innes, once the largest freshwater lake in NSW, was where Major Archibald Clunes Innes built his mansion along its shores. The grand house overlooked the impressive lake, with a thriving ecosystem that supported local Indigenous communities and early settlers.

In 1933, the lake was opened to the saltwater Lake Cathie in an attempt to drain it, causing saltwater to push further into Lake Innes altering the waterway's natural ecosystem.

Revive Lake Cathie has reported the fish kill in Lake Innes to National Parks & Wildlife Service, NSW Fisheries, the Department of Primary Industries and Port Macquarie-Hastings Council.

"Council has been undertaking weekly water quality monitoring at the Perch Hole, Lake Cathie (Ocean Drive) bridge and in the lower lake since January 2019," council director Melissa Watkins said.

"The most recent results from 28 May 2019 indicate salinity is around 46ppt at the Perch Hole and around 40ppt in the lower lake.

"Council currently does not monitor in Lake Innes. Lake Innes is managed by the National Parks and Wildlife Service.

"NSW Fisheries has advised council that they are aware of the reported fish kills and will be investigating.

"The stakeholders responsible for managing the entire lake system (NPWS, OEH, Fisheries and council) agree that the current conditions in the system are unlikely to change until we experience significant rainfall."

At its May meeting, council agreed to seek advice from the state government to find out whether, as a result of the Revive Lake Cathie submission, the Lake Cathie Opening Strategy should be reviewed.

"We are running out of time to support this dying ecosystem. Drought is not the only culprit responsible for the current crisis we are currently facing in the Lake Innes and Lake Cathie estuaries," Revive Lake Cathie president, Danielle Maltman said.

Revive Lake Cathie is planning a meeting with all stakeholders to help future-proof the lakes.

"Revive Lake Cathie is working towards providing conditions suitable for a sustainable ecological system by seeking implementation of historical report recommendations," Revive Lake Cathie board member Cara Dale said.

Revive Lake Cathie is calling for council to adopt the Revive Lake Cathie submission into its 2019-20 operational plan on June 19 at its monthly meeting. A contingent from the action group will attend the meeting whcih starts at 5.30pm.