The environment upstream of the salmon hatchery on Tasmania's Florentine River is pristine — it's a sought-after destination for fly fishers.
Downstream, it is a different story.
Tasmania's salmon industry has long relied on the state's freshwater rivers to operate its hatcheries, but the worsening presence of sludge, bacterial matting, and nutrients in the Florentine River has some sounding the alarm.
One of those people is local fly fisher Gerard Castles, who has previously been vocal about concerns with the salmon industry's operations in coastal waters.
Mr Castles contacted the Environment Protection Authority (EPA) after visiting the Florentine River earlier this month.
He has since sworn off fishing near the Salmon Enterprises of Tasmania (SALTAS) hatchery.
"I found white bacterial mats, I found a riverbed covered in a brown sludge, and I found white filaments floating through the water."
The EPA is looking into whether hatchery owner SALTAS — an industry and state government-owned joint enterprise — has breached its license.
"Water sampling indicates nutrient loads from the fish farm may be contributing to the algal issues in the river," a spokeswoman said.
The EPA said it was working with SALTAS on ways to remedy the problem.
The Florentine River feeds into greater Hobart's primary drinking supply.
The EPA said preliminary testing had not indicated concerns about Hobart's drinking water supplies, and further testing at the discharge site was done this week.
The hatchery is one of five industry facilities on the Derwent catchment that discharge wastewater back into the system.
Independent water quality scientist Christine Coughanowr said collectively, the discharge of nutrient-filled water from the hatcheries into the water system was similar to "several good-sized sewage treatment plants".
She said it was crucial to move away from flow-through hatcheries and instead use recirculated systems to protect Hobart's water.
"The Derwent particularly is a perfect recipe for algal blooms," she said.
"We have increasing nutrients, we have declining water flows, we have warming water temperatures.
Ms Coughanowr said once established, an algal bloom would be extremely difficult to eradicate, and could create issues with the drinking water supply if it was not properly treated.
TasWater has already committed to spend more than $240 million upgrading the Derwent's Bryn Estyn water treatment plant, partly to address taste and odour problems posed by algae further up the system.
Greens leader Cassy O'Connor said while taxpayers would fork out for the upgrade, the salmon industry paid very little to use the river water.
"We see that the river downstream from the hatchery is grotesque, what's growing in there is disgusting, and if people understand that that's the headwaters of their drinking supply they'll be very worried," she said.
The Greens are pushing for a parliamentary inquiry into water.
A SALTAS spokesman said the enterprise valued healthy waterways and "continues to work towards that".
"All operations are undertaken within the regulatory conditions, including monitoring programs and reporting."
