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Published: 2001-12-21 00:00:00

Environment Waikato has granted resource consent for Hamilton City Council to spray Hamilton Lake for weeds.

The City Council had applied to discharge the herbicides Escort and Roundup into Lake Rotoroa to eradicate yellow flag Iris and control the spread of water lilies. The herbicides will be applied from land and by boat by hand-held spot spraying over four weeks in autumn next year, with subsequent spot spraying in spring and autumn in following years.

The proposal attracted twelve submissions. The application included extensive community consultation and investigation into alternative options to the use of herbicides.

A NIWA scientist provided information on trials which had determined the most effective herbicide to remove yellow flag Iris. He said the die back of the Iris leaves would not cause an odour problem. An independent toxicologist said some individuals could develop hypersensitivity to chemicals and suggested that these people may wish to take specific precautions to avoid being exposed to spray.

Hamilton City Council is required to invite nearby residents to register with the City Council so they can be notified about 12 hours before spraying is to be done. Two Maori groups had given written approval.

In granting consent, the Hearing Committee expressed its concern at the length of time it had taken to action the removal of the yellow flag iris and the costs involved with the resource consent process. It recognised the potential anaesthetic and environmental benefits the proposal had for the lake.

The committee considered that the only other practical alternative available was mechanical removal, but this raised other detrimental environmental effects such as removing existing native plants, sedimentation and effects on water quality.

It considered the applicant had chosen the best practicable option currently available. It congratulated Hamilton City Council on its application, and said it appreciated the comprehensive and thorough case presented.