Cleaning mining pollution from river helps whitebait migrate home

Embargoed until: Publicly released: 2026-04-21 03:00

New Zealand

Kōaro from fish survey. Credit: Olivia Hore

Research commissioned by a mining company shows how removing pollution before it reaches waterways helped kōaro, a native whitebait, return upriver. The Ngākawau River in the West Coast was getting acid, metal, and sediment contamination from Stockton coal mine until treatment of mine water began in 2007. Surveys of fish in the river from 2005 to 2024 found just a few older kōaro present initially but, as water quality improved, lots more young kōaro - which swim up from the sea - appeared, and the population grew stable. The authors say it's important to keep treating mining pollution in water, which can act as a barrier to migrating native fish.

Multimedia

Kōaro from fish survey

Journal/
conference: New Zealand Journal of Marine and Freshwater Research

Research:Paper

Organisation/s: Pattle Delamore Partners, Instream Consulting, Bathurst- Talleys Mining Ltd.

Funder: This work was completed as part of paid professional services commissioned by Bathurst-Talleys Mining Ltd. The authors declare this relationship did not influence the research findings or interpretation.

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