My friends Louise and Andrew fly from Johannesburg to join me, and Tim drives us out of town and into the desert, past the Aswan High Dam and to a Lake Nasser dock. We board Yousef's launch, the Sobek, while a Cape Town couple, Dermott and Jennie Baigrie, embark on a second vessel, the Bushera. Our routine will be simple: Rise at dawn, fish, motor to a new part of the lake, fish, eat lunch, fish, and move on. In this vast waterscape dotted with granite islands and edged by sandstone cliffs and desert dunes, our boats double as casting platforms and tents. Moursi, the cook, pilots the Gazal, our double-decker mother ship, which holds the kitchen, bathroom, and shower—comforts designed for people who want to focus on nature, not five-star facilities. Moursi's cherubic assistant, Ali, provides the sound track, singing Nubian love songs for hours on end.

When I ask Yousef where he's from, he points at the lake surface and replies softly, "I come from down there." Completed in 1970, the High Dam drowned the ancient land of Nubia. Although the international UNESCO campaign to relocate Abu Simbel, Philae, and a handful of other monuments to high ground was successful, many Paleolithic, Pharaonic, Christian, and Islamic sites were lost underwater along with contemporary Nubian villages. Uprooted from ancestral homes, some 120,000 Nubians now labor in Kom Ombo's malodorous sugar mills or work in Cairo as domestic servants.

From the air, Lake Nasser looks like ink spilled over wrinkled parchment. The newborn ecosystem is still finding its balance, life returning in the form of wild geese or a calligraphy of cormorants flying low over the water. Cut off from civilization without maps or a satellite phone, ancient temples beneath us, I feel transported into a realm that seems timeless, apocalyptic, and pristine. Hydrologists estimate that silt carried down from equatorial African lakes and Ethiopia's Blue Mountains will fill the basin within five hundred years. A nanosecond from now, in geologic terms, the lake will die. Conceived as his everlasting pyramid and miracle of progress by the late president Gamal Abdul Nasser, the High Dam will have to be rebuilt.

The repository of the country's past, present, and future, Lake Nasser stores floodwaters that descend each July with the onset of the monsoon in Ethiopia's highlands. The government taps water at will, creating electricity for every town and village in Egypt and permitting year-round agriculture in a country that once spent unproductive months submerged. Stockpiling multiple flood years, the lake eliminates the natural cycle of high and low floods that in the past caused crop failure, famine, plague, and political weakness. Moreover, by the year 2017, the multibillion-dollar Toshka pumping station and canal, a megaproject begun by current president Hosni Mubarak, will be in operation and will, in theory, enable the government to reclaim vast swaths of western desert, liberating seventy million people from a thin green ribbon of Nile farmland and moving them into the unused ninety-six percent of the country.