A team of volunteers is helping to flush out poopers and litterers on the Milford and Routeburn Tracks.
Six Department of Conservation (Doc) volunteers began walking the Great Walks yesterday to combat a rise in illegal camping.
Huts and designated campsites on the Routeburn, Milford and Kepler Tracks are fully booked and unable to accommodate a rising number of walkers, and the department is concerned about freedom campers' impact on the environment.
Doc Wakatipu operations manager Geoff Owen said the campers were causing a problem with human waste and litter.
Although the problem appeared to be at a similar level to previous years, it could worsen next month, traditionally the busiest period.
The volunteers' main role was to gather "firm data'' on the issue and perform an educational role, Mr Owen said.
"People who are camping outside of the designated areas are also putting themselves outside of the Doc information network, so they may not become aware of changing weather conditions or if there any safety issues.''
Doc rangers were also taking an educational rather than punitive approach.
Although some were authorised to impose $300 on-the-spot fines for illegal camping, he was not aware of any fines being issued in the past few weeks.
The Routeburn and Milford tracks and huts are fully booked for the season, which ends on April 27, but Doc statistics show the number of trampers on its nine Great Walks has increased by 10% a year for the past three years.
Mr Owen said international marketing of the South's three Great Walks had "outstripped the supply to some degree''.
"They are very successful experiences, and you've got increased numbers as a result.
"The Routeburn offers people, in such a short timeframe, a complete outdoor experience from the lowlands to the tops.''
Day walkers spending unscheduled nights on the Routeburn were also contributing to the problem.
"People are pushing themselves [and] ... underestimate the time required.''
