"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.