Water quality has shown "improvement" in a remote Tasmanian harbour where an endangered fish is at risk of extinction and the future of salmon farming is under a cloud.
Macquarie Harbour on the island state's west coast is the only home of the Maugean skate, fewer than 1000 of which are believed to exist in the wild.
Federal Environment Minister Tanya Plibersek is reviewing salmon farming in the harbour after a challenge by conservationists who argue it is unacceptably affecting the species.
Departmental advice provided to Ms Plibersek called for a major destocking by last summer and found salmon farming was the main contributor to problematic dissolved oxygen levels.
Latest Tasmanian Environment Protection Authority data shows video seabed assessments underneath the farms were the "best on record" since the regulator assumed oversight in 2016.
The authority said in January all points at 35 metres below were compliant with environmental licence requirements.
It described the dissolved oxygen data as encouraging, saying some deeper harbour areas were approaching guideline values, which were calculated before levels went south in 2009.
"I am cautiously optimistic that environmental conditions in Macquarie Harbour are improving," authority director Wes Ford said.
Salmon Tasmania and the Liberal state government say the data is proof the industry and the skate can co-exist and management efforts, including pumped oxygen, are working.
But conservationists are not convinced.
"It is like saying we have one cool summer so climate change is over," Bob Brown Foundation campaigner Alistair Allan said.
"A natural event occurred in Macquarie Harbour that wasn't predicted ... there was an influx of oxygenated water.
"That is a lifeline for the skate but not for Salmon Tasmania."
State Minister for Industry Eric Abetz said the data confirmed the government's view that the industry should continue.
"Our position is absolutely clear: we unequivocally back salmon jobs around Tasmania," he said.
"Requests to reconsider the existing environmental approvals for salmon farming in Macquarie Harbour have no sound basis."
A spokeswoman for Ms Plibersek said the department was reviewing more 2500 submissions as part of the request to overturn the approvals.
"The government is carefully considering the information and scientific advice to ensure a proper, legally robust decision," she said.
A $7 million two-year trial is using a barge to draw up water, fill it with oxygen bubbles and pump it back into the harbour.
A second stage of the project recently began in which oxygen loads of up to 1500kg a day are delivered.
"What (the EPA data) shows is that the environmental health of the harbour and salmon aquaculture are not mutually exclusive," Salmon Tasmania CEO Luke Martin said.
Mr Ford said the data provided a "foundation for further improvements" through the pumped oxygen project.
