West Harbour Community Board member and Pūrākaunui resident Duncan Eddy said the damage occurred in the last week of October.
"I’ve never seen this kind of carnage on the salt marsh before — it’s really sad."
The Pūrākaunui salt marshes had been "badly carved up" and many local residents were "gutted", he said.
"People need to realise that the Pūrākaunui salt marsh is an important ecological area, not a place for hooning on dirt bikes."
He had been contacted by people concerned about dirtbikes on the beach and estuary for months, but said the damage in October was the worst he had seen.
Mr Eddy was not aware of any further damage to the salt marshes, but said anyone who saw motorbikes on the beach or estuary should contact the Department of Conservation.
In 2022, Pūrākaunui Block Inc signed the Ngā Whenua Rāhui covenant with Doc which provided funding to regenerate and protect Māori-owned land.
"It’s actually not a road, and it’s not a paddock — it’s a salt marsh, and it’s not designed for vehicles," chairwoman Nicola Taylor said.
Doc Coastal Otago operations manager Gabe Davies said it was disappointing to see the damage.
"The area has high cultural and ecological values. Salt marsh areas support important vegetation and bird species and are a valuable nursery ground for some fish species," he said.
Pūrākaunui Inlet was frequented by coastal wading birds and extensive meadows of ureure, or beaded samphire, grew there.
