The Amazon

Of all the rivers in the world, the Amazon carries the greatest volume of water—one-fifth of all river water—and has the largest drainage basin—5 percent of the world's total land area. In 1994, researchers claimed to have discovered its true source as the Ucayli River, and, if they are right, that may make the Amazon also the world's longest river, surpassing even the Nile. Its discharge—up to 7,000,000 cubic feet (196,000 cubic meters) per second—is so strong that it carries fresh water 200 miles (320 kilometers) into the Atlantic Ocean.

More than 1,000 streams make up the Amazon's tributaries, at least 20 of which are more than 600 miles long and are major rivers in their own right. They include the Ucayli, the Tocantins, the Xingu, the Tapajos, the Madeira, the Purus, the Jurua, the Javari, the Huallaga, the Maranon, the Trombetas...