Visitors are littering the Milford Track with toilet paper and human waste.
A Department of Conservation (DoC) contractor told Radio New Zealand the amount of human waste visible was "disgusting" and that the situation was getting out of control.
"On some of the Great Walk tracks, you find poos and toilet paper just littered down the side of the tracks," the contractor told Radio New Zealand.
"In some of the campsites along the Milford Road, it's really quite bad, you've only got to walk 20m into the bush and it's all over the place."
The contractor said the Milford Track was getting busier each year, and that many tourists did not understand how to use a toilet.
"At some of the DOC campsites, even though there are toilets there, for some reason some individuals only use the toilet paper and they'll poo outside the toilet," the contractor said.
"It's just disgusting."
DoC recreation manager Richard Davies said it was only a small number of tourists who were causing problems.
"We learn from every summer, but we can't be everywhere at all times," he told Radio New Zealand .
"For whatever reason, there's always been a minority of people who don't do the right thing."
He says DoC was working to build more toilets on the track.
They'll also be increasing the number staff on duty to address any issues, and urged the public to get in touch if they saw any poo on the track this summer.