The illegal opening of a river in south-west Victoria has led to a massive fish kill, almost exactly 15 years after a previous illegal opening killed 30,000 fish.
Authorities are investigating the incident in the Surry River at Narrawong, which took place on Wednesday night.
Glenelg Hopkins Catchment Management Authority (GHCMA) staff said "many thousands" of fish are dead in the latest incident and that number is still climbing — but it is hoped the death toll won't match that of the July 2005 fish kill.
GHCMA chief executive, Adam Bester, said it appeared someone had dug a trench through the sand bank between the Surry and the ocean.
"I can't go into details at this stage because it's under investigation but we do have physical evidence [showing that] a channel was built between the sea and the river," Mr Bester said.
"We were expecting, based on the rainfall coming through, that the river should have likely opened [naturally on Thursday].
"But based on when it was observed to be opened, which was between 6.30pm and 8pm [Wednesday], there was no rainfall or no increase in flow through our gauging station so we know there was no change in flow that would warrant the opening to occur naturally."
Significant fines for illegal opening
Mr Bester said it took the Surry River years to recover from the last fish kill.
At least one local farmer had complained to local politicians about flooding caused by the unopened river, and is claiming the river opened naturally.
Mr Bester said that was definitely not the case, and that the person or persons who illegally opened the river could face "significant fines".
He said opening the mouth of the Surry River at the wrong time caused the high quality water with the optimum oxygen levels to flush out to sea, leaving fish with poor quality water and leading to a fish kill.
A natural opening caused by rainfall typically allowed the water to mix, preventing a loss of only the high quality water.
GHCMA is conducting a clean-up and says the full size of the fish kill won't be known for days.
