Twists and turns in a tale of hippos on islands of papyrus

The Nile is the world's longest river. Its longest branch, the 6,000km White Nile, flows from unknown springs in Rwanda and Burundi, through the great lakes of central Africa and the world's largest swamp, in the forgotten vastness of southern Sudan.

But its biggest flows, especially during the annual flood, come tumbling out of Ethiopia's Lake Tana as the Blue Nile, which joins the main stem at Khartoum. From there, the combined river flows to the great man-made lake behind the High Aswan dam, through Egypt and on to the Mediterranean.

Except that, thanks to humanity's huge demands on the river, the Nile rarely ever reaches the sea. It gives out in myriad irrigation canals on the delta. And the river is getting shorter by the day. The huge volumes of silt, eroded from the parched highlands of northern Ethiopia, are mostly now captured behind the great dam, gradually filling its reservoir. The silt no longer reaches the river's delta to fertilise fields or replenish soil lost to the waves of the Mediterranean. As a result, the delta is being washed away by the sea. Already several kilometres are gone, and salty sea water is penetrating ever further inland.

In fact, as Robert Collins points out in this excellent biography of the river, it is stretching a point to call the Nile a river at all downstream of the Aswan dam. Really, it is just an irrigation canal for its last 800km. The dam gives the Egyptians total control over the river beyond that point. And they use it to discharge just enough water to keep its irrigation canals full while holding the rest of the annual floodwaters back in case of drought or to generate hydroelectricity.

From the earliest civilisations, Egypt has been defined and nurtured by the Nile. The river and the great dam that now dominates it have made Egypt, one of the driest nations on earth, one of its most profligate water users.

The country consumes more than 3,000l of water a day for each of its 60 million inhabitants. So great is the apparent abundance that nobody cares that a tenth of the river's flow - about 10 cubic kilometres of water a year - is lost from the surface of Lake Nasser, the reservoir behind the High Aswan dam. That's almost as much water as flows into the English water-supply system in a whole year. Collins tells the story of the river with forensic care, but also with passion and encyclopaedic knowledge. It is a compelling epic about a river he knows intimately, from almost half a century's study and travel. And not just in Egypt. This is the story of the whole river, from Rwanda and Burundi to the sea, and the 140 million people who share its waters. Collins has run its cataracts and penetrated the strange world of the Sudd, the giant swampland in southern Sudan characterised by papyrus islands that are large enough to carry herds of hippos, and of fractured pathways of the Nile that are still powerful enough to destroy the islands and crush the beasts by the dozen. Collins has interviewed the region's politicians, read its history and understood its hydrology, its ethnography and its engineering. He is as good on the motivations of its engineers as on the hydrology that ensures that, however much or little water flows into the Sudd each year, precisely 16km3 flows out. There is no better guide. And all in 230 pages.

Such brevity will entice many readers to learn more. I was left fascinated by the trinity of British engineers who lorded it over the river at the turn of the century. There was the extraordinary engineering genius of Christian evangelical William Willcocks, who imagined and designed the first Aswan dam and later, refusing to go home to England, became "a pernicious nuisance to the imperial establishment". There was William Garstin, perhaps the British empire's greatest hydrologist, who came up with a plan to drive a canal to take the Nile on a bypass, avoiding the Sudd swamps, where half its flow is lost to evaporation. And Murdoch MacDonald, who saved Willcocks' Aswan dam from being scoured away by the Nile as it passed over the dam, but who, for his pains, was forever afterwards hated by Willcocks.

From the days of the pharaohs to today, no river has so dominated a nation as the Nile dominates Egypt. Should the river ever fail, then Egypt would fail. The country is virtually rainless, and its people rely almost totally on the Nile to live. Stray far from the river and, give or take the odd oasis, there is no life. Nothing. The Greek historian Herodotus called Egypt "the gift of the Nile"; that remains true today.

Fred Pearce is a freelance journalist.