And a place to begin is with the obvious, with the fact that most of the life on earth depends on fresh water. The mineral earth with its dream shapes of mountain range and valley basin, desert and forest and taiga and prairie and butte and mesa, forged by the heat of the earth's core, scoured by the advance and retreat of glaciers, terminated by coastal cliffs and beaches of sand or shingle, is intricately veined with the flow of it. The story of our relation to it begins, I suppose, with pieces of bone excavated along the Awash River in Ethopia and a piece of a jaw excavated beside an ancient lake in Kenya. Ardipithecus ramidus and Australopithecus anamemnsis: they are about 4.4 million years old. At one point eight million years ago, a welter of hominid species foraged the edges of the same lake. And among them, most likely, were our ancestors. Human life probably developed within easy range of lakes and rivers. Human civilization—at the Tigres and Euphrates, the Ganges, the Yangtze, and the Nile—certainly did.

Human beings must first have used rivers for drinking and bathing and for food, fishing the shallows and hunting the birds and mammals drawn to the banks for water. It was probably fishing and hunting on floating logs that led to boat-making, and boat-making must have increased enormously the mobility of the species. Agriculture developed in the rich deposits of the flood plains. And these sedentary toolmakers were soon harnessing the power of the water with mill wheels and dams. Irrigation, as a technology, is about three thousand years old. It will tell you something about the stress human beings have put on river systems in the last hundred years of this history if you know that in 1900, 40 million hectares of cropland were under irrigation world-wide. Forty million hectares in three thousand years. By 1993, 248 million hectares were under irrigation.

It's also a fact of the twentieth century that as a mode of travel, for commerce and pleasure, rivers have been largely displaced by highways, railways, and air travel. A hundred and fifty years ago the epic stories of engineering had to do with canal building, connecting one river system or one sea with another: Panama and Suez. The locks of the Erie Canal and the extensive lock system of English rivers belong now to a quaint and minor tourism. The stories of the twentieth century have had to do with massive dams, with nationalism and economic development and the prestige of massive dams. Rivers now supply 20 percent of the world's electrical power, most of it generated by large, ecologically destructive, often culturally destructive, dams. The still-to-be-completed Three Gorges Dam on the Yangtze is only the latest in a series of Faustian bargains technological culture has struck with the rivers of the earth.

Though the names are still magic—Amazon, Congo, Mississippi, Niger, Plate, Volga, Tiber, Seine, Ganges, Mekong, Rhine, Colorado, Marne, Orinoco, Rio Grande—the rivers themselves have almost disappeared from consciousness in the modern world. Insofar as they exist in our imaginations, that existence is nostalgic. We have turned our memory of the Mississippi into a Mark Twain theme park at Disneyland. Our railroads followed the contours of the rivers and then our highways followed the contours of the rail lines. Traveling, we move as a river moves, at two removes. Our children don't know where their electricity comes from, they don't know where the water they drink comes from, and in many places on the earth the turgid backwaters of dammed rivers are inflicting on local childen an epidemic of the old riverside diseases: dystentary, schistosomiasis, "river blindness." Rivers and the river gods that defined our civilizations have become the sublimated symbols of everything we have done to the planet in the last two hundred years. And the rivers themselves have come to function as trace memories of what we have repressed in the name of our technical mastery. They are the ecological unconscious.

So, of course, they show up in poetry. "I do not know much about gods," T. S. Eliot wrote, who grew up along the Mississippi in St. Louis, "but I think that the river is a strong brown god." "Under various names," wrote Czeslaw Milosz, who grew up in Lithuania along the Neman, "I have praised only you, rivers. You are milk and honey and love and death and dance." I take this to be the first stirrings, even as our civilization did its damming and polluting, of the recognition of what we have lost and need to recover. When human populations were small enough, the cleansing flow of rivers and their fierce floods could create the illusion that our acts did not have consequences, that they vanished downstream. Now that is no longer true, and we are being compelled to reconsider the work of our hands. And, of course, we are too dependent on our own geographical origins to have lost our connection with them entirely.

Traveling in the world, even now, we confront, one way or another, the human history of rivers. Several times in the last few years I've arrived in a foreign city, and gone to sleep in a hotel room, and awakened to look out the window at a river. The first time was in Budapest. The river was the Danube. I woke up just before sunrise, walked out onto a balcony, and in the cold air at first light, looked out across the Pest hills and the first glimmerings of day on the broad, mud-colored water. The smell of it was in the air. I realized that I didn't know much of its geography. I knew that it originated somewhere in the Alps, flowed east across southern Germany—the Nibelungenleid consists of Danube river tales—and south from Vienna through Hungary and then southeast again through Serbia, emptying into the Black Sea somewhere south of Odessa. I seemed to recall, vaguely, that the poet Ovid, when he offended Caesar Augustus, had been exiled to a half-wild garrison town at the mouth of the Danube. And I knew that a few years before, a particularly mindless plan to dam the river as it flowed across central Hungary had become so controversial that the government outlawed public discussion of the project by scientists.

The lights were going out on the bridges, I could make out the dim forms of a few barges on the river, and a voice drifted toward me on the wind. There must have existed and perished in five thousand years whole dictionaries of river slang in half a dozen different languages, Magyar, and several German and Slavic dialects, and whatever hybrid Romanian is. There must once have been a Romano-Serb or a Romano-Germanic river pidgin spoken by merchants and boatmen the whole length of it. And it may have been in Roman times that it acquired its common name, since the Romans were great makers of maps, though it had probably been, long before any legions marched along its banks, a local god in many different cultures, with many different names. I knew of one poem, by the Belgrade poet Vasko Popa, that addresses Father Danube in a sort of Serbian modernist prayer. Belgrade—belo grad—means "white city" in Serbian:

O great Lord Danube
the blood of the white town
Is flowing in your veins

If you love it get up a moment
From your bed of love—

Ride on the largest carp
Pierce the leaden clouds
And come visit your heavenly birthplace

Bring gifts to the white town
The fruits and birds and flowers of paradise 

The bell towers will bow down to you
And the streets prostrate themselves
O great Lord Danube

I did not bow down. I found myself instead up to my neck in the comedy of consumer travel. I had called room service and ordered coffee the moment I woke. It arrived in a silver pitcher with a cream-colored china cup and a saucer with a fluted rim. I poured the coffee and then thought to check the bill. As near as I could tell, it was going to cost me $30, and this occasioned in me mild panic. The staff spoke English; I considered calling them and telling them there had been a mistake; I didn't require what the menu called a "morning beverage," after all. The problem turned out to be my arithmetic. The coffee was $3—but when I went back out onto the balcony and sipped the coffee, which smelled like wine and unripe berries and dark earth, and watched the Danube turn silver in the dawn. I thought I was drinking a $30 pot of coffee. It was a kind of offering to the river god.

The second time I looked out such a window the river I saw was the Huangpu. I had also come into Shanghai in the dark. This time I woke to a pearl-grey morning hazy with river mist. The river itself was teeming with traffic—barges, sometimes two or three together, linked by thick cables, carrying lumber, sacks of cement, girders, building tiles; tankers low in the water, ploughing against the current; tugs; packed ferries; a few sailboats; other ancient and non-descript vessels. In five minutes I counted eighty going and coming. The water was grayish-brown, foaming against the embankments, quays, warehouses, and docks. Just below me a crowd of people and bicycles was queuing for one of the ferries. Across the river was the Bund, the old commercial street of the pre-World War II city with its European-style bank and insurance buildings and hotels in the shapes of Greek and Roman temples, old coal-smoke-darkened marble columns and domes. Shanghai, I learned later, is a relatively modern city. In the fourteenth century, the Bund had been a tow-path for river barges above a reedy wetlands and a small fishing village. The village became a town in the sixteenth century. By the end of the nineteenth, it might have been the commercial riverfront of any European river city—Lyon or Glasgow or Amsterdam.

The street at that hour was already aswarm with the flow of human traffic and it seemed to mimic the movement on the crowded river. It was as if I were looking out not at another continent but another time. The river was a nineteenth-century river, thick with the traffic that had elsewhere in the world been transferred to trains and air freight, and sixteen-wheel trucks. The Bund—most of the buildings dated from 1880 to 1920—was a living memory of the forms of European piracy that came to be called “the Age of Empire.” I half expected to see Joseph Conrad emerge from one of the buildings in his Edwardian beard, carrying a commission to captain a steamer up the Congo. But the scene also looked like a Chinese scroll painting, as if the jagged line of Maoist-era apartment buildings in the distance were mountains, and the river-mists the half-remembered forms of local and dynastic gods, and the river itself an allegory of human life: provision and supply, upriver struggle and downriver flow, and human crowds coming and going in a smudged and dreamy haze.

There was also something unsettling about the scene, and it was not until later in the day, as I was wandering around the city, that it dawned on me what I had seen. Or not seen: I turned abruptly around and traced my way back to the river, leaned against the embankment, and stared a long time. There were no birds. Not a single gull, no ducks, no herons or egrets. Not a cormorant or a grebe. There were not even sparrows or songbirds in the spindly trees in the riverside park. And there was not a fisherman in sight. The river, for all its human vitality, was dead.

The third river was the Nile. Even at night, from my room at the Semiramis in downtown Cairo, there was no mistaking it, though I couldn't make out that fabulous stream itself. Laughter, some of it good-natured, some of it hilarious, floated up to my window. Brilliant lights all along the riverside seemed to mark bridges and a promenade and open-air cafés. And there was the smell of it, even in the humidity and auto exhaust, green and cool. It was there in the morning, in the unbelievable din of Cairo traffic—it seemed in Cairo that not honking one's horn was the exception rather than the rule—and even in all that noise it looked peaceful: greenish water; a strong, gentle current; reeds; palms; bankside banyans with their broad gleaming leaves; and, as if conjured from a late eighteenth century water color, the red lanteen sails of the felluccas, skimming upriver in a following breeze.

Nilus is probably no older than any other of the discontinued river gods, but he is older in the human imagination, a fact that was demonstrated to me the next day when, quite unexpectedly, I ran into an old friend in the hotel lobby, an American woman living in London. She was in Cairo for one day only. She was about to get into a cab to go have a look at the Ben Ezra synagogue, the oldest in the city, which she needed to be able to describe in a novel she was working on. On an impulse I joined her. The cab driver assiduously honking his horn so that we could only communicate in shouts, we threaded our way through the streets. The previous day had been an Islamic holiday, celebrated by a daylong fast, followed by the butchering of a live animal at sunset, goat or sheep, and a feast—to commemerate, we had been told, the sheep sacrificed by Abraham when the Lord God spared the life of his son Isaac, once Abraham had established his willingness to kill his own son for this deity. It meant that the corners of the Cairo streets were stacked with the still-bloody pelts of skinned animals, in which the flies were conducting their own festival, and that, once we were out of the car, in what is called Old Cairo to distinguish it from the other old Cairo, the Islamic city of the middle ages, the cobblestones were slick with reddish or tea-colored puddles where the blood had been washed from the streets. We made our way across the street gingerly; wandered down an alley out of the novels of Mahfouz, which smelled of mint tea and apple-wood smoke from tiny cafés; and came to the open courtyard of the synagogue, which was closed.

My friend had to settle for a description of the exterior of the building. A man rose from one of the café tables across the square and approached us, gestured solemnly with two raised fingers for us to follow him, which, somewhat hypnotized, we did. He took us around to the other side of the building, where, in a garden of palms and what looked like antique fuchsias, there was a well, covered with ornate ironwork. "Here," he said, "Moses was found in the bulrushes." We both balked. "Here?" "Oh, yes," he said—within a few days I was to understand that the city was full of these scholars of local legend—"this was the old channel of the river. It flowed straight through here. Moses was a Cairo boy." There was no Cairo in Pharaonic times, but Memphis was only thirty miles upriver, and the river did once flow this way, so who was going to argue the point? Not far from the synagogue is Babylon, a ruin—a wall of brick and rubble—of the Roman fort from which the city of Cairo grew. A renegade band of Persian army deserters had established a settlement there in the sixth century B.C., and their fort, later, in Trajan's time, came to serve as the foundation of the Roman fort. Memphis and the Saqqarah pyramids were just twelve miles south. And if the infant of a Jewish slave had been placed in a basket made from the wicker of river reeds, it may very well have floated downriver to this spot. The probability, at least, would have invited the legend, and it is quite possible that some of the descendants of those Jewish slaves were among the founders of a holy place inside the walls of the abandoned Roman fort that had turned it into an enclave of Jews and Coptic Christians two thousand years ago.

The Aswan High Dam, built in the 1960s by the Nasser regime as a monument to national independence, has had the unintended consequence of eating away the foundations of these old buildings. The dam captured the flow of nutrient-rich silt that created Egyptian civilization so that it was no longer deposited downstream and made farmers dependent on chemical fertilizers. The backed-up waters spread schistosomiasis through the communities of the Upper Nile and allowed the Mediterranean, as it seeped inland against the weakened current, to wash away almost entirely the Nile delta and its lucrative fishery, and the diversion of water to marginally arable lands forced the city of Cairo to draw down its freshwater aquifers. The result is that the salts underground are rising and eroding the foundations of Cairo's ancient mosques, churches, and some of the pyramids themselves.