A $150,000 upgrade of Silver beach, Kurnell, that was completed just this month has been vandalised.
Four recently planted young tuckeroo trees were chopped in half and destroyed.
Sutherland Shire mayor Steve Simpson described it as a "destructive act" and said the trees would be replaced.
The trees were planted as part of an upgrade of the area made possible through an agreement between Sutherland Shire Council, Sydney Water and the Water Delivery Alliance after the delivery pipeline was laid for Kurnell desalination plant.
Councillor Simpson said the new trees were placed to minimise view loss and community consultation helped determine the final design.
"The trees will be replanted at a cost of more than $4000," he said.
"This destructive act is being investigated by council, as are options for passive surveillance to deter vandals [from] reoffending.
"Anyone with information is asked to report it to the council.
"It's a shame that this great beachside area has been marred by an act of thoughtless vandalism."