The City of Fredericton and Department of Environment officials are investigating the illegal cutting of about 20 trees along the bank of the St John River.
The damage was discovered on Friday morning in the area of Waterloo Row and Grey Street, said Fredericton's forester, Don Murray.
"It's basically a trespass, cut on city property, and some of these trees have been dropped in the river," he said.
"It's quite upsetting that someone would do that, because it's a destruction of the habitat. And the root systems on the trees are what's holding the riverbank in place. And loss of the trees means this river could basically creep back onto the Green down here," Murray said.
"Our next step here is that we've got to come down and remove this debris and we're looking for a planting program, probably for next spring."
If the culprits are found, they could face charges and be forced to pay for the clean-up and re-planting, said Murray.