Dawn at Lake Rotoroa Lodge and King Kong breath wreathes the sheer, forested slopes. I stand on my balcony drinking coffee looking out over where the Gowan river slides from the lake with the lethargic viscosity of ice-cold vodka. If I looked out on this every morning for a hundred years I don’t think I’d tire of the view.

A trout rises and the concentric ripples move downstream in slow motion. I’m tempted to run down and try for it again ? last night I was out there until I was casting by starlight ? but I haven’t time. It’ll still be there later.

On the ferry I shiver in an early chill turned bitter by our 30-knot progress across this ribbon of black water towards a point where the Gothic peaks cascade into two ravines, and the D’Urville and Sabine rivers feed frigid water to Lake Rotoroa. We start up the Sabine valley on a trail that leads into the mountains, but after only 10 minutes cut left to meet the river. The trail is narrow, winding through scrub and trees. A warm clearing opens and closes in again, and then we are on the open river plain ? dry, littered with dead trees, the stream rattling along clear and fast. Black flies swarm and the sun reflects sharply off white boulders. We have no idea whether we’ll find trout as the river hasn’t been fished this season. Scott has, with the understatement of a Kiwi, prepared us for a day of fruitless slogging.

We set up and walk for a long time. The pools are thin and clear. Light shines through the surface on to a bed of copper, gold, red and white rocks. We’re looking for grey or brown ghosts in the marbled kaleidoscope. Every pool has promise but is empty. We walk for an hour before Scott sees it lying in shallow water by a fallen tree. A large, grey shape flicks in and out of focus, moving like a candle flame guttering in the wind, like all the other shivers and reflections on the stream bed. My first cast lands right by the fish, and I wait for it to bolt. I’ve learnt that the fish are wired like motion-sensing mines. A flash from the rod, a heavy footstep, a clumsy cast ? anything can set them off.

But this trout holds and I get another chance. My next cast is off line, the one after too far. I slow down, breathe and finally land the fly on line. The yarn dips and the fish is on. It isn’t enormous ? perhaps 4lb ? but this trout, this pool and this valley are utterly as I had imagined trout-fishing in New Zealand to be, so close to perfect.

Even so, it is hard to abstract ? from a week during which every fish, every river has burnt into the memory ? the defining moment. Maybe that fish in the Sabine, but that is only one of a hatful of trouty perfections, an album of animated postcards.

“It’s blue up there,” Peter says, though outside is thick with fog. We meet Greg, our guide, drive for an hour to Springs Junction and wait as the last vapours of mist melt. The sky behind is an infinite blue. Peter pushes me towards the front seat, by the pilot. “You sit up there. It’s quite a ride.“

Dozens of superb trout streams lie within striking distance of Lake Rotoroa Lodge: the Wairau, the Sabine, the D’Urville, the magnificent Buller and a bunch of other secret and stunning rivers I can’t name lest the guides take out a contract on me ? all of them an easy drive or boat ride; the Gowan I could walk to. But Lake Rotoroa Lodge is at the northern end of the Southern Alps, on the edge of an immense, temperate rainforest, and many more streams are days on foot from the nearest road. The only way to reach them is to clear the diary and walk or to book a chopper. Peter had a special river in mind.

The cockpit curls around me like a goldfish bowl as we crawl up the side of a mountain, the rock face only yards away. We cross the ridge and the mountain suddenly drops away, a sheer fall that makes my stomach lurch, the ground dropping into shadow thousands of feet below. A crescent lake in the shadow reflects the sky and looks like a polished sickle dropped on to folds in a dark blanket.

The small stream comes drumming down through a pavement of white rocks, its course lying within the sculpted braids of a bigger, angrier river, now dry. It was the home of truly enormous trout, including the Lake Rotoroa Lodge record, a cast of which hangs behind the bar. There was something reptilian about that fish’s gaping jaw, distended belly and immense size. It was caught with half-a-dozen mice in its stomach, in a year when the beech nut cycle exploded the mouse population and fattened the fish to abnormal obesity. If there’s a river worth flying to, Peter told me, it’s this.

The chopper drops us in a clearing of long grass where the river licks along the belly of a mossy wood. Right away we see two trout, fat blimps tethered side by side, shifting to and fro in the current. One heavy footfall, one rolling stone splashing into the riffle below the pool and they are gone. At the head of the pool another grey hull rocks from side to side in the current. Every so often a disc of flat water passes over the top, the fragmented shape comes together and we see how big it is. Greg and Peter hang back while I panther up the bank. I try a dry fly, but the fish doesn’t even look at it. I try another pattern, then another.

The downstream wind picks up, and soon it is difficult turning the long leader over on target. The trout rejects each fly I throw at him. Finally Greg ties on a yellow caddis. The cast drops 2ft to the side, but it’s the fly the trout wanted all along and this time it moves decisively across the river, turns and takes the fly, chasing it downstream. I lift the rod as Greg lets out an almighty and sustained howl to strike, a howzat of a cry that tears the quiet valley in half. The noise echoes off the valley walls and my fish is on the line, a slab of a trout that pulls like a cart rolling downhill.

Its adipose fin smothers my thumb as I pose for a picture; the caudal and pectoral fins hang down like the paddles of some plesiosaur emerging from a primeval swamp. What an amazing fish! Greg reckons it’s only 6lb or 7lb, but that it would push 10lb in a mouse year. Mice or no mice, it’s the biggest brown trout I have ever caught.

It stayed that way for a day. The next day we found large numbers of big fish on one of Scott’s favourite streams near the lodge. Scott and Andy were pulling out one after the other on deep nymphs while I took pictures. Later I crossed the river to see whether I could get the light from behind, but I got cut off in the shadows between two deep channels.

I walked up the ridge looking for a way out, but stopped at a flicker. Something to my left tucked against the bank. Patches of sun camouflage the water surface, but there’s a fish-like shape in the water. Or is it a rock? I decide it’s a rock. Then, 6ft upriver, a trout rises, its black snout pushing up a delicate bow wave. The trout is vast. It’s hidden in shadow, but glides occasionally through a shaft of sunlight, taking seconds to pass through the beam of light. It rises occasionally to flies I cannot see.

Scott and Andy have drifted upriver, nearly out of sight round the next turn. My trout is still rising, though I’ve put most of the patterns in my fly box over his nose. Only once does he push against the underside of my fly, but nothing else so much as stirs him. The water is cold. I haven’t moved my feet for ages and I’m starting to shiver. The fish needs a smaller pattern, size 18 or 20, but it would seem absurd to tie one on such heavy tippet.

After 40 minutes I have nothing to lose and I give it a go. It looks like a full stop on an anchor chain. But at my first cast the black submarine rises inexorably to eat it. I time the strike and have him on ? a crocodile trout attached to a tiny, barbless hook. How the hell am I going to get it in? I shout, but the sound only echoes. I need to get the fish to the tail of the pool where I’ll have a chance of beaching it. Below that is a 100yd chute of white water.

I keep the trout under as little pressure as I dare. It tires itself holding station in the faster water. I hold it steady until I sense it weaken and lead it gently to a shallow hollow on the edge of the stream, where it lies on its side calmly in 4in of water and the hook drops out. I’ll never know what it weighed, but yesterday’s fish would have fitted inside it.

There was no progression in this trip, no quest, no story-line meandering to fishy triumph or failure ? just day after day of the best trout-fishing on the planet. I couldn’t get enough. One beer down, with the light going, that trout rising in the icy vodka bothered my cocktail hour all week. On the last evening, after the end-of-season party, beer on my own seemed too indulgent. The trout took a sedge and leapt in the air, skipping over the water in the gathering dark. It fought like a sea-trout, broke my line and left me to find my way back in the pitch black.

I stayed at Lake Rotoroa Lodge and fished with the lodge’s dedicated team of guides. The Edwardian lodge is a great place to stay ? really comfortable with spacious rooms overlooking a stunning view of Lake Rotoroa. There is a bar where guides and guests can share a beer at the end of the day. The sitting-room with its open fire and engulfing leather armchairs is profoundly relaxing. The food is awesome and the wine list extensive. You can really spoil yourself here.

Lake Rotoroa Lodge is run by Shackleton International. Call Brent Hyde on 0064 3 523 9121, or email the lodge.
Book through Frontiers, The Dovecot Workshops, Barnsley Park, Cirencester, Gloucestershire GL7 5EG. Call Justin Staal on 01285 741340, or email him.
Arrange international flights to Christchurch and internal flights to Nelson. A lodge vehicle will collect you from Nelson airport.

Fishing

The lodge’s team of guides ? all friendly, patient and great company ? know the country well and can get you on to the best rivers. The lodge can arrange chopper flights at extra cost.

Tackle check-list

– At least two rods: 9ft 5-weight and 9ft 6-weight.
– Floating WF or DT line to suit. If your line isn’t dark green then dye it before you go.
– A basic selection of flies: Czech-style caddis pupa and bead-head nymphs,
various colours, various weights and various sizes from 12 to 18, deer-hair sedge patterns, para-Adams and Klinkhammers sizes 12 down to 20.
– Breathable waders and felt-soled boots.
– Top-quality Polaroids such as Maui Jim.
– A supply of white yarn stuffed into a film canister to tie strike indicators.
– Gink floatant.
– Maxima tippet (guides sniff at anything else) down to 3lb breaking strain.