A Wellington wildlife sanctuary is preparing to poison one of its dams as it tries to return the lake to a pre-human state.
The naturally-occurring chemical rotenone will be used next week at the top of the Zealandia sanctuary's upper dam to eradicate about 100 brown trout that are cannibalising native fish.
It's the first time in New Zealand rotenone has been used in flowing water.
A boat has been removing about 100 native banded kokopu fish from the lake ahead of the poison drop.
Zealandia's conservation manager Raewyn Empson says the sanctuary has had great success in removing pest mammals and weeds, and the operation on the waterways is the realisation of a 15-year dream.
Ms Empson says if the project works in the upper dam, the sanctuary plans to try to eradicate about 10,000 perch from another lake below.
