Vandals have destroyed about 25 native trees recently planted along Barongarook Creek near the Girl Guides Hall and Colac Police Station.
The offenders pulled the trees and stakes from the ground and threw them into the creek only days after Council planted them.
Manager Services and Operations Dave Thornburg said the vandalism had undermined efforts to improve the local environment.
"These trees will provide long-term environmental and community benefits, so it is disappointing to see them destroyed so soon after planting," Mr Thornburg said.
"Acts like this damage public assets and divert resources away from other important community projects."
Anyone with information is encouraged to contact Colac Police.
Council has also identified unauthorised bike tracks on the steep embankment along the same area of the creek and will remove them due to creek bank damage and the safety hazard they pose.
"We ask everyone to respect our parks, waterways and public spaces so they can be enjoyed by the whole community," Mr Thornburg said.
