WANAKA, New Zealand -- Lewis Verduyn gestures with an oar. "To pick tea from a tea tree," he says, "take the older growth, not the tips. You don't want to damage the bush."
We fan out across the riverbank and gingerly begin to gather the dark green leaves. Verduyn moors the raft, then heats river water in his Volcano, a hollow flask filled with burning twigs. For a few blissful moments, the only sounds are the crackle of the fire and the rushing of the great, green, glacier-fueled Upper Clutha River.
We hear the jet-boat before we see it. A growl swells to a roar as the yellow and purple monster bursts around a bend in the river. We stare as the boat flashes past. How can they see anything at that speed? Then we're alone again.
My children, Owen, 11, and Anna, 9, watch Verduyn, a wiry outdoor type with a wry sense of humor, as he whirls a pail of tea around his head.
"It must be seven times, for flavor," he says. "We have a strainer, because even in the wilderness, you can still be sophisticated."
We savor the refreshing brew, and our idyll is restored. Almost. Because if Verduyn and his bittersweet tea show why New Zealand is a must-see for ecotourists, that jet-boat is a symbol of how everything could turn sour.
Tourism in New Zealand is booming. In the last six years, international visitor numbers have risen 41 percent. But that success poses challenges for a country whose unique selling proposition in the global tourism market is spectacular, unspoiled nature. We found New Zealand's outdoor activities and wildlife outstanding, but under pressure.
Akaroa, where we start our visit to New Zealand, is typical of the ecological treats the country has to offer. The harbor of this pretty seaside town is the collapsed crater of an extinct volcano, 20 miles across. This is the site of the first -- and last -- French settlement in New Zealand, founded in 1838. It's also the calving ground of the rare Hector's dolphin, the smallest dolphin species in the world.
Durelle Bingham started Akaroa Harbour Cruises with her husband, Ron, in 1985. They've been running dolphin trips since 1991.
"It seems to be fashionable in England to swim with dolphins before you die," she says. "It topped the list in a survey. We're happy it did."
Our launch sets off across the bay, the rugged rim of the crater looming above us. The sky is grey; Owen and Anna wear two wet suits each. Our skipper tells us the aim is to let us mingle with a pod of dolphins, but we're not to disturb or touch them, and we won't swim with mothers or calves. Minutes later, we're bobbing in the chill water where the crater opens into the Pacific Ocean. A mile away, the barren shore plunges into the sea.
The dolphins weigh a maximum of 105 pounds, with black and white markings and a unique, rounded dorsal fin. It's thrilling to have them swimming near us, in pods of three to six, but hard to see beneath the choppy surface of the water. After several dips and a couple of hours, we're back on board, exhilarated but cold, clutching mugs of hot chocolate as we head for shore.
Wildlife pops up in unexpected places in New Zealand. At the Woolstore Cafe in Oamaru, the homemade cakes are delicious and the apple juice the finest I've tasted. The surprise comes when proprietor Carol Burns pulls up one of the floorboards to reveal a blue penguin burrow, complete with penguin and a very fishy smell indeed.
As dusk falls, we visit the Oamaru Blue Penguin Colony nearby to watch the diminutive creatures, also known as little or fairy penguins, come ashore. Denis, our guide, says the colony started 13 years ago with a few nesting boxes in a deserted quarry. Now there are 180 boxes in an area planted with native trees and shrubs.
Denis has his work cut out, because for a long time the only animals in sight are Boris and Snugget, two resident fur seals -- impressive, but not why we're here. Just after 10 p.m., Dennis calls for silence.
"The first group of birds is off the coast now, about 100 meters out to sea," he says.
Suddenly, the water roils with penguins. There's a moan of excitement from the crowd, and a chorus of shushes. Then a group of 25 penguins appears, waddling up from the beach right in front of us. More appear: 21, then seven, then 30, massing as if for an attack. The penguins are in no rush. They stand at the top of the shore so long that the viewing platform starts to empty. By the time the stragglers disperse into the undergrowth, we are alone, looking out into a clear, fresh night.
Perhaps the best way to get close to nature in New Zealand is to put one foot in front of the other. At Lake Manapouri, we hire a rowing boat to cross the Waiau River and embark on the four-hour Circle Track.
At once, we are swallowed by a primeval forest. Everywhere, ferns unfold like alien seedpods. Huge fungi climb up rotting trunks. We hear the trickle of water and the cries of birds.
At the summit, we eat our packed lunch looking out over the mountains of Fiordland. A South Island robin hops up, as if to demonstrate the fearlessness of New Zealand birdlife, and sits watching us from within arm's reach.
That evening, I meet Julia Wolfrum, a nurse from Hamburg, in the campsite kitchen. She has just completed the Kepler Trail, one of New Zealand's Great Walks, a set of government-maintained hiking trails in the country.
"The isolation and silence are magic," Wolfrum says. "When you're hiking, all alone, and it's getting dark, you imagine things. It's like a fairy tale sometimes. The nature makes you feel like a child again."
Up the road in Queenstown, nature is in full flight.
Queenstown advertises itself as "The Adventure Capital of the World," where you can bungy jump, heli-ski, jet-boat, or sky-dive. The confines of the modest town can no longer accommodate the throng of thrill-seekers. Soaring mountains still fringe the lake, but condos are creeping along the shore, a snake of traffic clogs the road into town, and Louis Vuitton has set up shop along with Global Culture, a clothes store.
If your idea of a holiday is a seething mass of cars and people, topped off by a cacophony of helicopters, Queenstown may be for you. Otherwise, it serves only as a warning of the perils of overdevelopment.
"Queenstown used to be nice, but it's a mess, now," Verduyn says, as we continue our trip down the Upper Clutha. "We don't want to get like that."
He points out a bunker-like private dwelling atop a bluff, and shakes his head.
"It was a disaster to put that building in there," he says. "People from all over the world are coming here seeking a wilderness, a sanctuary. The worst-case scenario is that we damage the environment, which brings people to New Zealand in the first place."
Leigh Turner is a freelance writer in Berlin.