Discoloured water at the upper reaches of Lake Eucumbene has raised questions about water quality. Photo: Chris Dawson.
A report of discoloured water entering Lake Eucumbene from the Tantangara transfer tunnel has raised concerns about potential impacts on fish spawning, water quality and Adaminaby’s drinking supply – but authorities say there’s no evidence algae-affected water was transferred during a recent bloom.
The matter was first raised on 27 April by Canberra resident Chris Dawson, who said he noticed unusual water conditions at the upper reaches of the lake, where the Eucumbene River enters from the tunnel linking Tantangara Reservoir.
Mr Dawson said his observations were based on time spent on the water rather than formal scientific expertise.
He said he fished the Eucumbene system regularly throughout the trout season and had spent considerable time around the inflow where the Eucumbene River enters the lake via the Tantangara transfer tunnel.
“Over the years I’ve become very familiar with that section of the lake and its usual condition,” he said.
“I’ve only once previously observed what appeared to be blue-green algae in that area at the level or concentration I recently encountered, particularly in the flow path entering from the river and around the portal discharge.”
He said his concern was not simply the broader presence of algae, but what he believed was a concentration of material entering and accumulating in a key inflow zone.
“That area supports spawning movement, aquatic food chains and forms part of the broader water storage system,” he said.
The Eucumbene River system is a key spawning area for brown trout during the cooler months, when fish move upstream and eggs and juvenile fish depend on clean, oxygen-rich water.
Mr Dawson said his concerns extended beyond fishery, to Adaminaby’s drinking water supply, which is drawn from Lake Eucumbene.
“This is not just a fishing issue,” he said, “it is an environmental issue, a public health issue, and a community issue.”
His observations follow a red-level blue-green algae alert issued by WaterNSW in March for Tantangara Reservoir and sections of the Murrumbidgee River – indicating algae levels high enough to pose a risk to people, livestock or pets exposed to untreated water.
Map showing Lake Eucumbene and Tantangara Reservoir within the Snowy Mountains Hydro-Electric Scheme. Image: Wikipedia/Snowy Mountains Scheme.
Monitoring for blue-green algae is coordinated by WaterNSW, which publishes alerts when levels pose a risk to untreated water users.
Sampling is carried out regularly across regional waterways, major dams and popular recreation sites, with increased frequency during periods of elevated risk.
WaterNSW said the March alert had since been lifted as conditions improved, and there were currently no warnings in place for Lake Eucumbene.
While its primary purpose is hydroelectricity and water storage for the Snowy Mountains Scheme, Lake Eucumbene is also one of Australia’s premier trout fishing destinations and a major recreation hub.
It also remains Adaminaby’s drinking water source, though supplies are treated to meet Australian drinking water guidelines and are generally considered safe.
While the earlier outbreak related to Tantangara and downstream river systems, the two storages are connected as part of the Snowy Scheme, meaning water can be transferred between them through a network of tunnels and infrastructure.
That link has raised questions about how water quality is managed across connected reservoirs.
Snowy Hydro said it undertook regular water quality monitoring under its Snowy 2.0 management plan and maintained communication with relevant agencies when blooms occurred.
The company confirmed water transfers between Tantangara and Lake Eucumbene were halted during the March algal bloom, and later resumed after the alert was lifted.
It said testing had indicated the bloom had dissipated, with results now below national alert thresholds, and that any discolouration observed in releases was likely due to residual material left behind after the earlier bloom rather than the presence of active algae.
“Algae are a natural feature of Australian waterways and are increasingly common in many lakes and rivers due to warmer temperatures and high nutrient levels in late summer,” a spokesperson said.
The NSW Environment Protection Authority (NSW EPA) said it had reviewed monitoring data from Snowy Hydro and found no evidence linking algal activity to Snowy 2.0 construction.
It also confirmed transfers were halted during the March red-alert event before later resuming in line with the Snowy Water Licence.
The EPA said it reviewed water quality data weekly under additional monitoring requirements introduced in 2023, alongside standard monthly reporting, but reiterated it did not have the authority to direct or suspend transfers between the two storages.
Those transfers are governed by the Snowy Water Licence under the Water Management Act 2000, which is administered by the NSW Department of Climate Change, Energy, the Environment and Water (DCCEEW), a separate regulator to the EPA.
Mr Dawson said he had raised his concerns directly with the EPA, but its response left him with ongoing questions about oversight of water management decisions.
“It appears the EPA has virtually no authority to influence the decisions of Snowy Hydro with respect to water management,” he said.
