A trickle runs through it

Simon Cain would rather be a trout bum, but he's busy helping our chalk streams to heal themselves. By Andrew Brown. Photographs by George Wright

On the river above Salisbury, little dark flies are hatching off the river, and small trout are chasing them with as much fuss as if they were popping champagne corks. It is one of the classic English landscapes - except that the river is disappearing. Three thousand years ago, the giant megaliths of Stonehenge were floated to this bend before being dragged the last two miles to the temple site. Now you could hardly float a bathtub in the water.

Simon Cain is a man who mends rivers. He would rather be a trout bum: for years he fished his way round the world. Then he settled on the upper Avon, near Salisbury, and started to build bamboo fly rods. It is the sort of countryside that rock stars buy when they have everything else (Sting's mansion is just up the road); and the river Avon that runs past it is one of the classic English chalk streams, where the trout are as plump and picky as the men who own the fishing.

But the great chalk streams of England are shrunken trickles of their former selves, and anyone who really cares about them will find themselves learning a lot more than traditional fly fishing craft. In the past five years, Cain has become one of Britain's leading experts on the delicate business of helping rivers to heal themselves. He has worked for

millionaires who needed their estates improving, and for ordinary fishing clubs who just wanted their rivers rescuing. He now spends more time as a river consultant than fishing or even making rods. He draws up maps of a stretch of river, with the banks detailed down to the level that only ducks and fishermen see; and on these he plans his campaign before the troops go in.

Beneath the old stone bridge at Amesbury, Wiltshire, five middle-aged men can sometimes be found splashing around in chest-waders, hauling willow logs and bundles of hazel branches. They get to say "fuck" a lot more like this than they would in the office. They enjoy themselves, but they are also engaged in a deadly serious attempt to rescue a river that is being bled to death.

The Avon, like the Test and the Kennet, is a river fed by springs. The water is meant to flow steadily: it rises from innumerable sources on the chalk downs, which seep all year round into the broad valley bed. This ensures a steady flow of filtered, clear, alkaline water which is extraordinarily productive. Wild trout in such rivers grow to more than five times the size they do in the acid, fast-flowing streams of Dartmoor or Wales. At least that used to be true. But for the past 30 years, the rivers have been shrinking and speeding up, and losing their unique character. The River Kennet has shrunk by about four miles in its upper reaches: a stretch where 25 years ago I had to ford a waist-deep river to escape a furious landowner is now a dry depression in the meadow, without fish or the schoolboys to poach them. The banks of the Avon at Amesbury, which 40 years ago were water meadows, now stand two feet proud of the river; you can cross the main bed in Wellington boots.

The drought is only one reason for this slow change of character. Most of the damage has been done by cars, and the changes they have brought to the countryside. The spread of the suburbs has led to an inexorably rising demand for water, most of which is abstracted from bore holes in the chalk before it can ever reach the rivers: 75,000 new houses are planned for Wiltshire alone before 2015; 10,000 of them round Salisbury.

Some of the river menders feel this makes their efforts hopeless. "It's all bullshit," says Ronnie Butler, a prosperous businessman who as president of the Wild Trout Society took days off from the office to splash and haul with the best of them. "This is only an Elastoplast if they don't do something about the housing higher up." But, says Cain, there is no chance that these houses will be cancelled. They represent the aspirations of voters no one can afford to upset. The best that can be hoped for is a commitment not to build them without a sustainable water supply that comes from somewhere other than the irreplaceable chalk streams.

Even when they do not abstract the water directly, houses and roads damage the rivers in other, more subtle ways. Where once the rain that fell in the valleys was slowly filtered through fields and water meadows to the river, it is now collected in gutters, and dumped all in one go into the rivers, which thus lose the even flow that was one of their main distinctions. This has been going on since roads were first metalled to speed cars on their way.

Against these threats, the river menders try to ensure that the water that is in the rivers does as much good as possible. This means narrowing the bed, and putting the curves back in. Curves in the rivers concentrate the current, which make deeper, shaded holes for trout, and a cleaner river bed. They also help to speed the current up, which promotes the growth of ranunculus, a long, white-flowered weed like mermaid's hair which is one of the defining glories of a chalk stream.

The work at Amesbury is being funded, for the first time, by the Environment Agency, which put up half of the pounds 10,000 it cost to repair a stretch of river around 350 metres long. The rest of the cost is borne by the Salisbury and District Angling Club, which owns the rights to the water, and the Wild Trout Society, a newly formed pressure group which proposes to agitate in chest waders.

The basic building material is willow, available on every bank. Reinforcing a stream bank with willow logs has a doubly beneficial effect, for the trees when alive suck water out of the river at a tremendous rate. Each one can drink 100 litres of water a day. In the water, they are laid in arcs away from the side of the bank and back. These are then built into small artificial islands with faggots of hazel bound with wire. The river completes the work when it floods, by wedging all the cracks with weed and vegetable matter, which become larders for innumerable small shrimps and insects. Within a year, the work looks immemorial, as if it had been done by God when he discovered dry fly fishing. The river becomes deeper, narrower, and faster. The broad pale silty shallows disappear, to be replaced by alternating deep pools and rippling stretches of ranunculus.

In the resulting paradise, only man is vile. For much of the damage to the original chalk stream ecology has been done by greedy fishermen. The wild trout have in many places almost been driven out by stocked fish, often rainbows, which grow faster than brown trout and so make more profit. The Wilton club water, on which some restoration was done last year, is the longest stretch of chalk stream left that is managed for wild trout. There are stretches on the Avon that are not too heavily stocked; and when the club which owns the fishing at Amesbury surveyed the water before starting work, they were astonished and gratified by the number of wild trout they found. But when fishing can be let at up to pounds 200 a day, the pressure is great for owners to stock fish that clients with that sort of money can catch - big, stupid, and not very strong. Even when they stock brown trout, these are not often the river's native strain. If these rivers are ever again to be home to as many wild creatures as they held even 50 years ago, there is an enormous amount of work to be done; but at least a start has been made