Most research sources agree upon the three longest rivers in the world. They disagree upon the official lengths of these rivers and which rivers would fall into what ranking after the top three rivers are named. The dispute over length comes from what the source determines is the beginning and end of the river. Some would say the end or mouth of a river should be determined by where the coastal tide no longer affects the river. Some say the beginning or headwaters of a river is where the river is first called by its name. The Ordnance Survey in Great Britain begins its determination of river length at the mouth of the river and travels toward the headwaters, following the larger of any two tributaries when they come to them. This is the reason that no two lists of the world's twenty longest rivers will agree except in the top three rankings.
The longest river in the world on every list is the Nile River of Africa. Sources give its total length as between 4,132 to 4,180 miles. The Nile River has two main tributaries, the Blue Nile and the White Nile. The Blue Nile's headwaters are in Uganda at Lake Victoria; the White Nile's headwaters are in Ethiopia at Lake Tana. The two tributaries unite at Khartoum in Sudan. The Nile and its tributaries flow from the highlands and mountains in central Africa to the low-lying delta in Egypt where the main river spills into the Mediterranean Sea. The river name comes from a Greek word "Nelios" which translates into River Valley. It was the presence of the Nile River Valley that allowed the ancient Egyptian civilization to arise and prosper. The Nile River provided water for agricultural and economic development and transportation.
The river coming in at number two on every list is the Amazon River of South America. Its total length is said to be between 3,920 to 4000 miles. Unlike the Nile River, the Amazon stretches itself from east to west. Its headwaters are near Calillona, Peru and its delta in northeastern Brazil pours into the Atlantic Ocean. The Amazon River floods during the rainy season and expands beyond its three to six mile width. The river is important to the native cultures living along it and helps to support the lush rain forest flora and fauna. The first non-native to travel the length of the Amazon River was Spaniard Francisco de Orellano in 1542. His was a rather hurried flight after a skirmish with an Amazonian tribe along the upper part of the river. The Amazon figures prominently in John Grisham's novel "The Testament" and is one of the rivers visited by author Marty Essen and his wife in the book "Cool Creatures, Hot Planet: Exploring the Seven Continents".
No disputes are made over the Chang Jiang or Yangtze River of China ranking third on the list of longest rivers of the world. Its total length is said to be between 3,915 to 3,964 miles. The Yangtze begins in the Kunlun Mountains of Qinghai Province. It empties into the East China Sea just north of Shanghai. The official beginning of the river is at the city of Chongqing (Chungking) where two large tributaries unite after plummeting from the Tibetan mountains. The Yangtze River was a natural boundary between ancient northern and southern Chinese kingdoms because it was very difficult to cross. Chang Jiang translates as "Long River". The nation of China is building a huge hydroelectric facility and dam called Three Gorges Dam with a completion date of 2009. Ten percent of China's electricity needs could be provided by this facility but 140 villages and over one thousand factories besides vulnerable flora and fauna species will also be destroyed by the project.
After these three major rivers are named, various lists rank other long world rivers in different arrangements. One river that is definitely one of the top ten on the lists is located in China. The Huang He or Yellow River gets its name from the silt it carries from its origins in the Kunlun Mountains to the mouth at the Gulf of Bohai. Its length is listed as 3,394 miles.
The Ob-Irtysh River of Russia is also on the lists. The first 310 miles of the Irtysh River flows from its source in the Altai Mountains, through China, then through Kazakh Republic until it meets the Ob River in Russia and proceeds through Siberia to the Gulf of Ob in the Arctic. It is listed at 3,362 to 3,459 miles in length. For five or six months of the year, the Ob-Irtysh is frozen.
The Amur River of northeast Asia gets on the lists because of its 2,744 to 2,800 miles. The Congo of central Africa has a ranking as well, being between 2,718 to 2,900 miles in length. Some lists try to combine the Missouri and the Mississippi Rivers of the United States and list the combined total length at 3,870 miles. Other lists put the Mississippi at number fourteen at 2,350 miles and the Missouri at number fifteen at 2,341 miles.
The top three rivers, though, and where they rank in a list of the longest rivers of the world are not in dispute.