Horizons Regional Council says it is investigating earthworks on the banks of the Whanganui River, where dirt and tree stumps were seen being pushed into the river.
In images sent to the Chronicle by a concerned member of the public, a digger can be seen clearing a portion of land on the river bank.
The member of the public, who did not want to be named, said she was kayaking up the river on November 8 when she noticed the works.
"It just seemed a little strange - I would've thought there were some serious environmental concerns there."
The person said a "decent chunk" of the land was pushed into the river in the short time she was there, as well as some rocks and old tree stumps.
"This just seemed very strange.
"This part of the country is beautiful, and the river is clearly pretty special to people. I would've thought work like this on the river would be looked at closely, but it doesn't look like it."
A Horizons Regional Council spokesperson said from their investigation it appeared the works did not have resource consent.
"From our research, we do not believe there is a consent for this activity, however, we are also trying to determine the exact location, property owner, and work details so that our compliance team can investigate."
A council compliance officer who spoke to the Chronicle said the works looked "out of place".
Council compliance officers will be travelling to the site by boat in the coming days to investigate, the officer said.
The discovery of the work follows controversial earthworks earlier this year at a site also overlooking the river.
In February, protests took place at the Punakewhitu/Gentle Annie maunga after Horizons Regional Council granted consent to widen an access road to a forestry block, without consulting local hapū.
Those works saw a large chunk of the well-known maunga excavated, which Horizons later apologised for.