Lowering myself gingerly into the meltwater, my body is gripped by its cold embrace. Kitted out in thick wetsuit, mask and fins, camera securely in hand, I force in the first few breaths of air as frozen fingers of water dribble beneath my collar and claw their way down my spine.
As the temperature shock wears off, I am able to take in my surroundings. Large, moss-covered boulders lie amid banks of rough shale, all bathed in water that flows in pulses of colour. Pale green and clear, it changes in a heartbeat to a rich golden-brown, as clouds of peat are washed downstream by mountain rains.
Finning slowly forward through this bizarre chameleon atmosphere, I momentarily lose sight of the riverbed a couple of metres below, as another swirl of muddy broth sweeps past. Pausing for clarity, the visibility improves and, as it does, I find myself witness to an incredible sight. Ahead of me swims a solid wall of fish.
A thousand or more pink salmon are here in this Alaskan river, stacked one on the other in a tight school. Almost static, their lithe green flanks barely twitching, they hold position in the tide. Below the shoal, lying motionless on the bottom, are yet more salmon. The last remains of the early runners, their spent and scattered carcasses are left clinging to the waves of shingle. For them, the journey home is complete.
Nature has painted a surreal picture before me, for even in death these fish are magnificent. Resplendent in thick fur coats of mould, bathed in golden light, the dead salmon enjoy their final glory. Hovering above, the living are gathered, seemingly drawn together in homage to their fallen brethren, paying respect to those that have spawned to continue the circle of life.
Watching these scenes, it is hard not to feel a certain sense of mortality. I know that of the hundreds of fish before me, not one will live beyond the next two weeks or so. Salmon are anadromous; that is, they return to fresh water from the sea to spawn.
The word literally means up-running and thats just what these fish have done, swimming long and hard to return to this river, where they themselves were born. It was here that they lived out their infancy, before heading downstream to mature in the nourishing waters of the open ocean.
Such is the monumental effort required in returning to the spawning grounds of their home waterways, that once they have fulfilled their ultimate purpose, they simply burn out. Every last ounce of energy is spent conquering currents, rapids and waterfalls. This final push upstream to procreate inevitably ends in death. Many never achieve their goal, falling victim to fishermen, bears, eagles and exhaustion.
Closing in on the school ahead of me, camera pressed to my mask, I unknowingly cross the panic line, sending a thousand hitherto passive salmon into a frenzied burst of activity. The school erupts, silver-green torpedoes rocketing past me in every direction. The water boils with energy. Fish are leaping through the surface, gripped by fear of this black, bobbing intruder. Did I cause such excitement Sorry!
Gradually, as their panic subsides, the salmon begin rafting up into a school again. Packing themselves nose to tail, like the pieces of a complex jigsaw puzzle, the dense tangle of fins and tails locks into a whole, perfectly streamlined against the flow.
Hundreds of wary eyes view me with suspicion as I begin taking pictures, kiting back and forth in the tide, snapping off a frame on every pass. Each time, I try to sweep past a little closer for that frame-filling composition.
Its a slow process, but after half an hour, their confidence gained, I am accepted as one of the lads. With freedom to roam in the thick of the school, Im just one more pilgrim on the journey upstream.
As the irrepressible urge to spawn draws the salmon back to their home rivers, so their bodies begin to change. To conquer the fresh water and the rapids, to outswim their predators and competitors, a metamorphosis of body and mind occurs.
This is most evident in the large males, who undergo a transformation into grotesque caricatures of their former selves. No longer the svelte princes of the open ocean, large humped backs arch skyward, while wicked grins reveal a twisted rake of white splintered teeth. Their need now is to fight, not feed, and the gaping hooked jaws serve that purpose.
The annual Pacific salmon run is a grand spectacle. Witnessing it, one is struck by the strength of their instincts - a total and overpowering drive to spawn. All their energies are channelled to this purpose.
As the natural reserves are exhausted, so their bodies begin to break down, but the journey doesnt end here. The dietary tract, fins, scales and even the skin are all absorbed, tapping the valuable energy they contain. Before their inevitable death, many of these fish become zombies. Battle-scarred and weary, flesh rotting on their bones, they are the living dead.
This cruel parody of their former splendour is a testament to the rigours of a complex life-cycle, one that pushes these fish past the limits of physical endurance.