OVER the rubbery chicken at your next tourism symposium, challenge fellow delegates to name the world’s longest-running national tourism slogan. The answer—it was on the tip of your tongue—is “100% pure New Zealand”, Tourism New Zealand’s catchphrase since 1999. Why mess with a good thing? The notion of a country blessed with pristine land, water and air appeals not only to visitors. It goes to the core of what the country means to New Zealanders themselves. So the slogan has the “authenticity” such gatherings always call for.

New Zealand, wonderfully far from anywhere, really does seem to have it all: glaciers and jagged peaks, charismatic fauna, vineyards, lusty rivers for fly-fishing or rafting, dive sites and thousands of miles of glorious coastline—not to mention the cosmopolitan, foodie cities of Auckland and Wellington. Its genius, and that of its marketing campaign, is to appeal to everyone, from scruffy backpackers to silver-haired oenophiles and even the superyacht set.

Chris Roberts of Tourism Industry Aotearoa, a lobby group, says that the cliché is true: a visitor comes for the scenery but goes home talking about the people. That includes Maoris, whose hospitality is the flipside of their legendary warrior spirit. Many visitors experience a Maori welcome up close—the biggest tourism operator on the South Island is the Ngai Tahu tribe.

The number of tourists has shot up in the past five years, from around 2.7m to 3.6m in the year ending in June. Tourism has pipped the dairy industry as the biggest export earner. International visitors bring in NZ$14.5bn ($10.5bn) a year, the equivalent of over NZ$3,000 for each of New Zealand’s 4.7m people.

In particular, the number of Chinese visitors has nearly doubled in the past five years, to more than 400,000. A growing proportion are “free independent travellers”, as distinct from package tourists who don’t leave as many dollars in locals’ pockets. For Chinese from cities where pollution obscures the sky, a big lure is stargazing in the Aoraki/Mount Cook region on South Island, part of the world’s biggest “international dark sky reserve”. The tourism board still sees huge potential, claiming that 80m people are “actively” thinking about holidaying in New Zealand.

But there is a problem. New Zealanders are growing unsure about their country’s 100% pure image. One issue comes from the sheer numbers of tourists themselves. Another comes from the back end of a cow. Mr Roberts stresses that New Zealand sits way down the rankings of visitors relative to population and land area. But, he admits, some of the most popular tourist places are getting “hammered”.

The Tongariro Alpine Crossing, a day-long trek through spectacular scenery in New Zealand’s oldest national park, gets 125,000 hikers a year. Especially when a spell of good weather follows bad, not only the trail but the roads up to it are heaving. It is hard to control such congestion, since free and unfettered access to national parks, which cover more than a tenth of the country, is enshrined in law. A NZ$25m government grant to help local councils with such things as expanding packed carparks and public toilets will not go far.

A pall on the wild

Meanwhile, for many New Zealanders, it is all a big adjustment. Locals who used to have their favourite wild places to themselves increasingly feel jostled. A particular gripe is about visitors who hire camper vans without loos, leading to lots of what Indians would call “open defecation”. Traffic jams in resorts such as Queenstown, once unheard of, are another cause for grumbling. Even having to wait in a queue at your local café is an unwelcome novelty. One of the most open societies on earth still prides itself on its welcome. But 20% of New Zealanders say there are too many visitors—up from 13% who said that in 2015.

New Zealand’s pristine image has also boosted the dairy industry. Many Chinese consumers, in particular, choose Kiwi infant formula over domestic brands, which they fear will be contaminated. Over the past 15 or so years, sheep farms have been converted to dairy, and family farms snapped up by corporations—the so-called Queen Street farmers, named after Auckland’s main commercial drag. The boom has made fortunes. But it is also alarming New Zealanders who worry about the environmental impact, which has shot up the national agenda before a general election on September 23rd.

One objection is fragile landscapes ravaged to make way for cows, such as in the Mackenzie district, a dry upland rich in endemic plant and animal species that has been completely changed by irrigation. Conservationists are appalled that a rare ecology has been destroyed.

Indeed, water gets to the heart of New Zealanders’ concerns. Dairy cattle need a lot of it, and produce copious excrement and urine in return. This pollutes watercourses and fills lakes with algal blooms, despite new requirements to fence streams off from livestock. Some rivers have become too polluted to swim in.

Nitrates and microbes from faeces also seep into aquifers that supply drinking water in some places. The city of Christchurch, ravaged by an earthquake in 2011, lies to the north of the Canterbury Plains, where dryland farms have given way to heavily watered dairy operations. Christchurch draws its water untreated, which worries experts. Last year ago an outbreak of campylobacter in a suburb of Hastings on the North Island made 3,000 people sick and killed two or three. Some fear something much worse for Christchurch.

It has all struck a chord amid the election campaign. A larger-than-life sculpture made of manure that depicts the hapless environment minister, Nick Smith, defecating into a glass of water has been a hit. With images like that, it can’t be long before visitors notice there’s a problem in this pure, unsullied land.