Lake showing signs of recovery

Otago Daily Times

25-07-2025

Fix the catchment and you'll fix the lake.
That's the mantra the Friends of Lake Hayes has adopted to guide its efforts of nearly 20 years to restore the health of the picturesque lake between Arrowtown and Frankton.
Now that mantra is starting to bear fruit.
Since gathering an alliance of organisations around it — the Wai Whakaata strategy group — the Friends' members are starting to see real improvement, its chairman Mike Hanff says.
Wai Whakaata — the Friends, Kai Tahu, Queenstown's council, the Otago Regional Council and the Department of Conservation — is into its fifth year of implementing the Lake Hayes Vision study.
The study is a science-led plan of action for reversing the impacts of many decades of sediment runoff that's accumulated in the lake.
Hanff says since the "bad years" of 2018 to 2020, the amount of sediment flowing into the lake has reduced by about 75%.
The lake's water clarity is now the best he's ever seen, and is approaching a "tipping point" — which may be reached in five years — when the lake will be permanently clear.
He expects the toxic algal blooms that have made the lake unsafe for recreational use by people and dogs to become less and less severe before eventually stopping.
A series of interventions, which have cost an estimated $12million so far, are nearing full implementation.
They include the restoration of the wetland at the lake's northern end, the installation and regular clearing of sediment traps in the lake's main tributary, Mill Creek, and large-scale riparian planting.
Vegetation's been cleared from Hayes Creek — below the lake's outlet — to alleviate flooding at its southern end.
That's allowing another remediation measure that will start in September: piping water from the Arrow River irrigation scheme, near Macetown, to boost the flow of water into the lake.
The colder, denser Arrow River water will displace and help flush out the phosphorus-laden water at the bottom of Lake Hayes during the summer and autumn periods.
Hanff says a new policy in the district plan, which requires landowners in the lake's catchment to account for water quality in any development, is having a real impact.
That's been supported by the Friends' "non-confrontational" approach with landowners, getting alongside them to offer support and guidance.
Winton Group's Ayrburn is an example of the "amazing opportunities" for water quality improvements when developers take responsibility for their stormwater, sewerage and fertiliser outcomes, he says.
"We've never been anti-development ... we just want to help everyone in the catchment understand what they can do to play their part."
Hanff says continuing the "trajectory of improvement" will come down to how well landowners manage the 12 to 20 million cubic metres of water that runs off the lake's 42 sqkm catchment each year.
That's a massive swathe of land extending from the Mt Dewar-Coronet Peak ridgeline, across Speargrass Flat and Dalefield to the eastern suburbs of Ladies Mile, Shotover Country and Lake Hayes Estate, and around the lake's eastern side from Millbrook to Morven Hill.
Already one of the most studied lakes in New Zealand, it's now being intensively monitored, in real time, by a suite of sensors dangling from a buoy, and by sampling along Mill Creek that measure the water's sediment load, Hanff says.
"We know how much phosphorus is arriving in the lake every 10 minutes."
Through the Friends' work with Wai Whakaata, that data's showing the lake's health is going in the right direction, he says.
"But we've got to keep the foot on it."