At least 30 per cent more people are paddling and jetboating the Whanganui River this year than last, according to Whanganui conservation services manager George Taylor.
Department of Conservation staff had expected an increase - numbers have been increasing every year - but not one this big.
Raetihi-based Whanganui River Canoes owner Rebecca Mead said last year she would have had about 60 people on the river at this time - this year she has had 90 customers.
Josephine Haworth, at Pipiriki-based Whanganui River Adventures, said the Christmas/New Year period had been "really, really busy".
There are at least six jetboat operators on the river - two near Pipiriki, one at Atene, one at Whakahoro and two at Taumarunui.
Some of those jetboat operators are among the 10 businesses, mostly in the Ruapehu district, that hire out canoes. Of them at least four offer guided trips, with guides costing between $230 and $150 a day.
Adding to all this intense upper-river traffic are cyclists and trampers who need to be ferried around. There can be queues of boats waiting to put visitors ashore at the Mangapurua Landing where the track to the Bridge to Nowhere begins.
The busy season has meant some DOC staff have been diverted from other jobs to focus on the river, Mr Taylor said.
Weekends were the busiest, especially long weekends, and there are three coming up - the Wellington and Auckland anniversary weekends, and Waitangi weekend. Easter is also expected to be chocker.
There have been some accidents on the river in recent weeks, and the department has worked with police. Mr Taylor said he wanted people to come prepared.
"We ask that people are well informed, and they can get information from the website. We've also been working with operators to ensure their parties are well briefed."
The most likely reason for the busy season is heightened publicity about New Zealand's "Great Walks" in the past few years. The Whanganui Journey, though not on foot, is classified as a great walk, and the efficiency of its online booking site may also be an attraction.
The extra tourists put stress on facilities, and especially on sewage systems, Mr Taylor said. Increased numbers also changed the isolation experience of the river.
The department is about to begin the latest in a series of five-yearly surveys of river users. It will ask them about their journey and, after that, decisions may be made on limiting numbers.