A significant milestone’s been reached in Mana Tāhuna Charitable Trust’s continuing efforts to improve the water quality of Arrowtown’s Lake Hayes.

Mana Tāhuna’s been leading the way in a project restoring the picturesque lake, which has battled with pollution, with help from Queenstown’s council, Friends of Lake Hayes, e3Scientific and Department of Conservation (DoC).

Mana Tāhuna environmental projects manager Sarah Mukai says they’ve recently removed up to 500 tonnes of toxic sediment from its trap
at Mill Creek, a tributary to the lake.

Constructed on farmland owned by Chris Dagg, using DoC’s Jobs For Nature funding, the trap — the length of an Olympic swimming pool and about 20m wide — was completed last May, with a goal of decreasing the amount of sediment flowing via Mill Creek into the lake.

‘It’s working’: Mana Tāhuna environmental projects manager Sarah Mukai

Dubbed ‘Pukunui’, it’s the larger of two sediment traps in the area — the smaller ‘Pukuiti’ is downstream.

The traps comprise diversion channels with plastic sheeting and sand bags which divert water flow and pump out any remaining water, enabling toxic sediment, full of phosphates and nitrates from fertilisers commonly used in the 1970s, to settle before being excavated.

Mukai says the sediment’s responsible for algal blooms in the lake, and is particularly toxic to trout.

Additionally, Mana Tāhuna’s planted 63,000 native trees in the area, to help filter out the phosphates and nitrates in the water.

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