Scientists from Tasmania's Environmental Protection Authority say the latest monitoring data from Macquarie Harbour shows dissolved oxygen levels are close to the range in 2010 when levels began to decline.
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The monitoring data for sites in the harbour revealed a sharp decline in median oxygen levels in 2010 until late 2014.
This led the EPA to cut fin fish farming in the harbour by half in 2017.
The latest report on the monitoring data said the largest net improvements to dissolved oxygen levels had been observed since 2020.
"The observed decline in dissolved oxygen levels was less pronounced in the north-west section of the harbour and has shown the greatest improvement compared to dissolved oxygen levels within the central harbour and south-east section of the harbour nearer the Gordon River," the report read.
Oxygen levels further from the harbour mouth remained most outside the target range.
Parks and Environment Minister Nick Duigan said the report showed it was clear industry and research investment in remediation of dissolved oxygen levels in the harbour was working.
Salmon Tasmania in a statement said the report did not include the major Harbour recharge event that occurred in May this year; nor had the Macquarie Harbour Reoxygenation Project reached full scale.
"We have always said that it is possible to undertake salmonid aquaculture in Macquarie Harbour at the same time as protecting its natural environment, including the Maugean skate, and this is further evidence that the range of actions we are taking to support this are working," it said.
Environment Tasmania senior marine campaigner Rebecca Howarth said the monitoring showed that the Maugean skate's habitat still remained in the 'red zone'.
"It is misleading for the Tasmanian government to claim credit," she said.
Meanwhile, Hydro Tasmania on Friday announced it had completed catchment models for the King and Gordon rivers to show how water flows through the catchments and into Macquarie Harbour.
Executive general manager of assets and infrastructure Jesse Clark said while science showed river flows were not a primary cause of low oxygen levels, they could be part of a solution.
But he said river flows would not be a quick fix.
This is a complex system - it's not like turning a tap on and off," Mr Clark said.
"Pulling the wrong lever at the wrong time could inadvertently make the situation worse."
Political reporter for Australian Community Media, based in Hobart.
Political reporter for Australian Community Media, based in Hobart.
