A landfill near Fox Glacier which was partially washed away by last week's flooding is now littering nearby beaches with old rubbish for hundreds of kilometres.
Westland District Council said the landfill beside the Fox River was severely eroded in the flooding, with tonnes of rubbish taken downstream into the sea.
Rubbish has been found as far away as Okarito.
"Council has engaged contractors to undertake work on site to prevent further rubbish being exposed and taken downstream," the council said on Facebook.
"This is a temporary fix and will require long term works to make the site safe."
Volunteers from local towns are now in the process of picking up the scattered rubbish, much of which is plastic.
"In addition to this Council is working with the Regional Council, DOC and other agencies to formulate a plan to remove the rubbish from the environment.
"This is a significant issue and support from other parts of New Zealand is being sought."