The Queensland Greens say another fish kill in central Queensland could have been caused by dredging, despite the state government all but ruling it out.
The Department of Environment and Resource Management (DERM) is at a loss to explain what killed seven decomposing barramundi examined by its officers in the Boyne River on Tuesday.
Departmental officers travelled there to investigate commercial fisherman Chris Sipp’s report of about 15 dead barramundi in the river.
DERM director-general Jim Reeves said the fish bodies were decomposed and had probably been there for at least three days.
One showed signs of a skin lesion.
Because of their decomposed state it wasn’t possible to take samples of the fish to find out what killed them, Mr Reeves said.
Water samples of the Boyne River taken by DERM on the day found nothing out of the ordinary.
Mr Reeves dismissed dredging in Port Curtis as the cause of death, saying the fish kill site was more than 20km upstream from where dredging is being conducted.
“We are doing water tests there monthly and there’s nothing to suggest that there’s anything wrong with the water quality in the Boyne River,” Mr Reeves told reporters in Brisbane.
Barramundi and other fish began turning up in Gladstone Harbour with cloudy eyes, skin lesions and discolouration last year, sparking a three-week fishing ban.
Most fishermen blame a large-scale dredging operation but the government says last summer’s floods caused the problems.
Queensland Greens member and environmental medicine specialist Andrew Jeremijenko said there was “every possibility” the Boyne River fish kill was related to high turbidity levels in Gladstone Harbour that were recorded over the Christmas period.
The Greens say Gladstone Ports Corporation data show turbidity levels in the harbour were above normal for four days over the Christmas period.
There was scientific evidence linking acid sulphate soils and high aluminium levels mobilised during turbid conditions to fish deaths, Dr Jeremijenko said.
He said the fish could have swum through a dredging site, become sick and later died in the Boyne River.
“I don’t think they can say for certain that it’s not due to the turbidity in the harbour,” he said.
Deputy Premier Andrew Fraser said the Greens were having “a bet each way” by not accepting the work underlying the dredging’s environmental approvals.
“If it’s good enough to accept the science on climate change, then it’s good enough to observe the science on issues around Gladstone Harbour,” Mr Fraser told reporters in Rockhampton on Wednesday.
Gladstone Ports Corporation chief executive Leo Zussino said the high turbidity levels over the Christmas long weekend were caused by spring tides.
Some dredging was stopped for three hours on the outgoing tide as part of the corporation’s turbidity management plan, he said.
The corporation has approvals to dredge 46 million cubic metres from the harbour in order to expand the port for gas exports.
It wants the Great Barrier Reef World Heritage area to be redrawn to exclude the harbour.
News of the fish kill came as DERM announced the latest independent water quality tests in the harbour.
The tests showed no evidence that water quality was affecting fish health, or that dredging was causing environmental harm, Mr Reeves said.
Tests showed “a natural month-to-month variation” across testing zones, he said in a statement.
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