Lake Hayes remediation

The Otago Regional Council is investigating three potential methods towards remediating water quality in Lake Hayes.

The Council’s technical committee this afternoon took further steps towards remediating water quality in the lake, with three potential methods of flushing, capping and destratification under discussion.

The glacial lake near Queenstown has been suffering from ongoing algal blooms, caused by built-up nutrients in the lake bed. Studies have identified phosphorus from past industry and farming fertiliser practices as a key cause.

  • The flushing scheme would involve building a pipe to carry water from the Arrow irrigation scheme to Mill Creek to increase flows into Lake Hayes.
  • Capping would mean applying a chemical product to the lake bed to prevent the phosphorus there from rising into the water, spurring algal growth.
  • Destratification would involve using air compressors in the middle of the lake to continually mix up the water layers.

Potential methods show strong net economic benefits, but each approach has different benefits, costs and risks. The costs for flushing and destratification are estimated at about $400,000 over 10 years, though the cost of capping is dependent on the application method (between $90,000 and $550,000).

The Council intends to consult with the community later this year on the potential methods and how they could be funded.

“As part of our Long Term Plan process we’ve had strong feedback that progress towards remediating Lake Hayes water quality is an absolute priority for the local community. We’re happy to say that we’re making good progress,” Councillor Ella Lawton said. “It will be important from here to take the community with us as we move towards formal consultation. We’re looking forward to ongoing discussions to ensure that the Council and community have a common vision for the future of not only the lake but also the management of the wider catchment.”

Council Chair Stephen Woodhead emphasised that no method would offer a quick fix. “The potential methods are long term approaches – we’ll be looking at a decade or more to see significant progress.”

Work towards remediation is part of a multi-pronged strategy for Lake Hayes, Gavin Palmer, the Council’s Director Engineering, Hazards and Science said. Other aspects include a lake monitoring buoy and a detailed study of the catchment’s inflows, as well as initial works towards the potential flushing method. “With works shortly being undertaken by Millbrook, an opportunity presented itself to put some infrastructure in place sooner rather than later. We have confirmed today that work will continue towards putting in a pipeline that would enable flow augmentation.” Funding for the pipeline, which would be put in place in the coming months, was approved as part of the Long Term Plan process.