It's peak season on the Whanganui River, with about 100 people a day finishing river trips at Pipiriki.

About half of them are canoeists, with the rest "day trippers" who get rides in jetboats.
The campsites and huts have a booking system, and are at capacity.

Numbers using the river have been increasing about 15 per cent a year for the past few years, senior Conservation Department ranger Jim Campbell says. They have risen from about 4000 to about 9500 canoeists a year.

There are even more who are day visitors - many of them international tourists who don't have four days to paddle through the bush. All those people need a lot of toilets.

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On Tuesday's 1 News, Maori complained that some visitors were defecating in the bush rather than using toilets.

If people are "caught short", Maori would prefer them to bury their waste and keep it away from tracks and waterways.

Mr Campbell said the matter of bush toileting was an ongoing thing.

"You've got to show respect for the whenua (land). We don't like coming across it either."

People had complained that the toilets were smelling, and Mr Campbell said they sometimes did "smell a little bit" but there was no reason why people couldn't use them.

The department managed 32 toilets on the Whanganui River Journey, one of New Zealand's Great Walks, Mr Campbell said.

They are long-drop toilets, with waste dropping into a container and being flown out by helicopter.

It costs about $100,000 a year to manage all those toilets.

They each have a chimney, so that updraft can remove smells. But Mr Campbell said the river was renowned for being hot and windless, and sometimes there wasn't much draft.

The department could install solar fans to make the draft work better but that would make the toilets even more expensive.

It has installed a temporary toilet at the Mangapurua Landing to the Bridge to Nowhere, one of the most popular places on the journey. And it has a suite of four new toilets at John Coull Hut.

"We are continually looking at ways to improve those systems."

Mr Campbell didn't mind seeing an item about Whanganui River toilets on television.

"I saw it as a good way to publicise the river. It was looking beautiful."