Department of Conservation staff are poisoning 17 ponds, mostly on orchard and farm properties around the Motueka-Nelson area, to eradicate noxious gambusia (mosquito fish) and koi carp.
The poison being used, rotenone, has proven effective in the four ponds treated so far.
DoC conservation officer Tim Shaw said only a few of the tiny gambusia could be seen in the ponds before the poisoning, but when rotenone was introduced the water "came alive" as dead or dying fish rose to the surface.
The gambusia population was at its peak and Mr Shaw said there were many thousands of the fish in each pond.
Other fish and eels are removed before the poison starts. The eradication programme is expected to take three weeks.
Apart from killing the pest fish, DoC is using the operation as a chance to do scientific research on the effectiveness of rotenone and its antidote.
Mr Shaw said the antidote had proven effective in reviving some poisoned goldfish.
- NZPA
Pond pests poisoned
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