More than 30 trees near the Alexandra Bridge are dying after having been deliberately poisoned.
Otago Regional Council monitoring and operations manager Scott MacLean said an investigation yesterday confirmed 30 poplars and one willow tree were likely sabotaged.
"The trees all had drill holes in them, so we assume someone tipped herbicide in the holes.''
The poisoning has resulted in a patch of brown, dying trees on the Clutha River bank on the side opposite the town's CBD.
An ORC staff member looked at the area on Friday and carried out a more detailed investigation yesterday.
"We will be monitoring them because as they slowly rot they might become a safety hazard,'' Mr MacLean said.
"They may have to be cut down at some point, which is disappointing for the community - that their rate money might have to go towards this because of someone's stupidity.''
It could be difficult to track down the culprit as the trees could have been dying for a while, he said.
"Those holes could have been drilled months ago. I've heard stories about this kind of thing happening, but I haven't seen anything like it in the four and a-half years I've been here.''
Alexandra police had been notified of the incident, he said.
Mr MacLean did not want to comment on a possible motive.
Central Otago Mayor Tony Lepper said he understood why someone would want the trees gone, but poisoning was not the way to go about it.
"There are proper channels to go through. We felled poplar trees on the other side of the river last year.''
"Although the poplars are iconic to the area, I'd personally rather be able to see the river.''
Poplar trees near houses were dangerous, he said.
"I think any trees within striking range of houses shouldn't be there. But by poisoning them it only increases the danger.''
Alexandra police could not be contacted for comment yesterday.
