Mass fish kill in eastern Victoria due to salinity and other natural causes, authorities say
Regulators and water managers have blamed "natural causes" such as salinity for the death of adult carp in the main drain of Lake Wellington near Sale.
Advocates for the Gippsland Lakes said the mass fish deaths were just another indicator of long-term mismanagement of the waterways, while a scientist said the impact of the drought was to blame for the decline in water quality.
Phil Ronalds, who lives near Lake Wellington, a Ramsar-listed wetland, raised the alarm about the dead fish earlier this week.
He said diverting water from rivers for the nearby Macalister Irrigation District, and to supply Melbourne with drinking water, was part of the problem.
He said this fresh water kept the saline water at bay at Lake Wellington and across the extensive Gippsland Lakes network.
The Gippsland Lakes is a series of lagoons fed by seven rivers flowing down from Victoria's high country, towards the coastal town Lakes Entrance.
Much of the saline water that causes problems in the lake system is from the entrance being opened permanently to accommodate industry in the port.
Drought and summer bushfires contribute
Federation University environmental scientist Jessica Reeves blamed the current drought and summer bushfires for a decline in water quality across the lakes and increasing salinity.
"[With] rising sea levels, deepening of the entrance … and also the decreased rainfall, there just isn't enough fresh water coming in to dilute the system," Dr Reeves said.
"The overall salinity is increasing and particularly at the fresh water end such as Lake Wellington."
Dr Reeves has been doing research near Lake Tyers and said, because of the ongoing drought, its water levels were lower than people had seen in "living memory".
Confusion over cause of fish deaths
Southern Rural Water (SRW) manages the irrigation water from Glenmaggie Weir, which draws on water from the Macalister River, including the drain where the fish was found.
They were notified about the mass carp deaths on Tuesday, and informed Victoria's Environment Protection Authority (EPA).
"The EPA has confirmed this is one of several recent fish kill reports in the district, which are natural occurrences, typically caused by salt water ingress, not pollution," a joint statement from the two agencies said.
SRW spokesman Gavin Prior said the EPA ruled the carp deaths were from natural causes.
"How they died is not our decision," he said.
"Our [role] is to report our finding to the relevant authority and in that case it's up to the EPA to make that decision."
However an EPA spokesman told the ABC, SRW made the call about the cause of the dead fish.
A request to clarify this with the environmental watchdog had not been received before publication.
A Victorian Department of Environment, Water, Land and Planning spokeswoman said the agency helped clean a few hundred European carp, which died on the shores of Lake Wellington last week in a separate event.
Martin Potts, who works on wetlands for Greening Australia, also blamed the decline in the quality of the lakes on the drought and the diversion of water from the rivers, but said the death of carp was good for the lakes system.
However, he said mass deaths could cause further environmental problems and indicated native fish would also be affected.
"A large carp dying can deoxygenate a cubic metre of water," he said.
"We lose oxygen. [This] then causes a black water situation, so you can have quite a large lot of deaths all at once."
Editor's Note (15/4/19): An earlier version of this story incorrectly described Martin Potts as a Love our Lakes spokesman. He works for environmental organisation Greening Australia. The story has been amended accordingly.