Alexandra water pipeline expected to go ahead despite algae discovery


​​9 May 2019

A Central Otago District Council report released today​ is recommending that Council proceed with the planned pipeline from Clyde to Alexandra, but has red flagged a delay in the construction of the project's filtration system.

The review on the current state of the Lake Dunstan Water Supply Project was called for after the recent discovery of Lindavia algae, in Lake Dunstan, the species responsible for making lake snow.

The report will be considered by the Three Waters Infrastructure Committee at its meeting next Wednesday 15 May.

Central Otago District Council Executive Manager - Infrastructure Services Julie Muir says: "Our initial filter trials have certainly proved their worth. Finding out about the potential for lake snow now has given us the opportunity to alter our design brief for this project before significant investment takes place."

The new pipeline is due to be completed by mid-2020. An interim chlorination and UV process will be developed to treat water for potential bacterial and viral contamination, and will be ready for use before the completion of the pipeline.

Council will ensure the revised treatment design will not delay the delivery of a new water supply from Lake Dunstan to Alexandra.

Planning for the second stage (a filtration system to meet New Zealand Drinking Water Standards) has been delayed for at least 12 months until all filter trials are complete.

Council's initial trials using simple cartridges have unfortunately indicated disappointing results. The trial cartridge blocked within hours instead of the expected weeks or months. Upon microscopic examination the presence of Lindavia was confirmed.

The discovery of the Lindavia algae this early in the project will ensure that the final filtration system implemented will be able to treat water containing the algae. The findings from current filter trials will also be used to assist with project planning for the Cromwell Water Upgrade (scheduled for 2021).

Lindavia algae is the species responsible for making lake snow, a glue-like slime that blocks water inlets and water filters. This is the first time the algae has been found in Lake Dunstan. It has been causing issues for some time by blocking domestic filters in Wanaka and has also been found in Lakes Wakatipu and Coleridge as well as several North Island locations.

It is non-toxic and poses no known human health risk.

Central Otago District Council is not yet able to confirm the cost of implementing a new filter system and how this will impact overall project costs until a solution is finalised.

The Central Otago District Council is liaising with Queenstown Lakes District Council to share the costs and trials to identify a solution to the Lindavia challenge, which will impact many water sources across both districts. 

Page reviewed: 09 May 2019 2:16pm