At some 2,300 miles in length, the Mississippi is the longest river in the United States. At some 1,000 miles, the Mackenzie is the longest river in Canada. But these waterways seem minute in comparison to the world's two lengthiest rivers—the Nile and the Amazon.
The Nile, which begins in central Africa and flows over 4,100 miles north into the Mediterranean, hosted one of the world's great ancient civilizations along its shores. Calm and peaceful for most of the year, the Nile used to flood annually, thereby creating, irrigating and carrying new topsoil to the nearby farmland on which ancient Egypt depended for livelihood. As a means of transportation, the river carried various vessels up and down its length. A journey through the unobstructed part of this waterway today would pass by the splendid Valley of the Kings, where the tombs of many of these ancient monarchs have stood for over 3,000 years.
Great civilizations and intensive settlement are hardly associated with the Amazon. Yet this 4,000-mile-long South American river carries about 20% of the world's fresh water—more than the Mississippi, Nile, and Yangtze combined. Other statistics are equally astonishing. The Amazon is so wide at some points that from its center neither shore can be seen. Each second, the Amazon pours some 55 million gallons of water into the Atlantic; there, at its mouth, stands one island larger than Switzerland. Most important of all, the Amazon irrigates the largest tropical rain forest on earth.