Many rivers quenched the thirst of millions in the American west and around the world. Without these aqueducts, some of the earth's largest cities would turn into gigantic ghost towns.

Begun in 1817, the Erie Canal was an engineering wonder - 363 miles of water highway linking the western frontier to the Atlantic seaboard. It took eight years to construct and thousands of hours of brutal labor, but by the time it was done, 3,000 canal boats traveled the new corridor, making New York City a commercial capital.

Named one of the seven engineering wonders of the modern age, the Chesapeake Bay Bridge and Tunnel connects Virginia proper with its easternmost land mass. Stretching 17 miles across the historic Chesapeake Bay, the structure represents a man-made boundary between the Bay and the Atlantic. The structure includes two two-lane highways supported mostly by trestles, four man-made and one natural island, two truss bridges, and two revolutionary sunken tube tunnels.

In the land of Mardi Gras, jambalaya, and zydeco, exists an engineering marvel called the Lake Pontchartrain Causeway that seems to go on forever. Two ribbons of concrete span the largest inland body of water in Louisiana, and at nearly 23.87 and 23.88 miles long, these two spans form the world's longest automobile bridge. At midpoint--12 miles out--water surrounds travelers who are unable to see either shoreline. The bridge is so long, it actually transverses 1/1000th of the earth's circumference!

It stretches 2,500 miles from Boston to Miami. The Atlantic Intracoastal Waterway is comprised of a system of canals, land cuts, and a series of natural and artificial barrier islands, which provide a protected passage for low-draft vessels wishing to avoid the tumultuous currents of the Atlantic Ocean. The AICW was conceived in the late 18th century, before there was a system of roads in America. The numerous rivers, bays, and sounds along the eastern seaboard were the roads, and the Atlantic Intracoastal Waterway was envisioned to be America's first superhighway. Much like Route 66, the AICW represents a bygone era. A time when the transport industry was in its infancy, and life moved at a slower pace. It's a safe bet that the ships that sail its waters today value it for that very reason.

The world's largest concrete dam--and the largest concrete structure in the world--lies on the Columbia River in the State of Washington. Built in 1931, it is also one of the largest hydroelectric power plants in the world.

In 1954, Gamal Abdel Nasser, the Arab Republic of Egypt's first prime minister, had a plan to bring his poor country into the 20th century. To pull it off, he needed to harness the flow of the world's longest river--the Nile. The ambitious plan called for construction of a high dam in southern Egypt at Aswan. But the builders of the pyramids and the Suez Canal were no strangers to large undertakings. We'll see how the Aswan High Dam socially, politically, culturally, and agriculturally affected Egypt.

When completed, China's Three Gorges Dam will tower 607 feet in the air and weigh 40 Great Pyramids. Other than China's Great Wall, it will be the only man-made object visible from the moon. Supporters see it as key to a new China, controlling floods and bringing hydroelectric power to one of its least-developed areas. Critics voice a litany of concerns--from environmental to flooding the spectacular area for which it's named. We trace its story--from ancient flood control to current controversy.