In the last financial year, more than 117,000 people tackled the Great Walks (a 12 per cent increase on the previous year), with 60 per cent of them from overseas.
The revenue received by DoC from these visitors was just over $6 million but the cost of servicing them was just over $9 million. And that $3 million deficit seems only likely to grow.
As the Chronicle reported last week, it cost $564,212 to keep the Whanganui Journey open, but visitor fees only totalled $268.789 - and DoC says it does not have other options for charging people.
In other parts of the world, tourists pay to enter national parks but in New Zealand they are free. That has prompted discussion about ways of charging people who visit the parks.
However, differing charging systems at differing venues, possibly for different facilities, seems likely to cause confusion and probably create a costly layer of bureacracy which DoC and others could do without.
One answer would be a charge to international tourists when they arrive in the country.
An "airport arrival" tax would likely be accepted by most if it gave them access to New Zealand's natural beauty, and the money raised would help maintain the infrastructure which brought them here.