Is the Nile the longest river in the world? Amazon would like the word.

At a time when much of the world has been measured, and many arguments have been resolved – the highest mountain (Everest), the largest ocean (the Pacific), the most venomous snake (Western Taipan) – the question of which river is the longest in the world is still somehow out of our reach. What at first glance seems like a fundamental geographical question, a matter of cold science and hard numbers, has instead turned into a cartographic conflict that divided the scientific and exploratory communities along the fault lines of national identity, units of measurement and even personal anger.

The Nile - or the Amazon?

Sir Christopher Undatag, an English-Canadian adventurer who travelled to what he says is the distant source of the river, said, "The Nile is certainly longer than the Amazon. There's no doubt about that." Guido Gilli, former director of earth sciences at the Brazilian Institute of Geography and Statistics, responds, "The Amazon is longer than the Nile. I have no doubt in my mind.

Controversial science

It is not easy to answer this question. More than most geographical features, rivers are constantly changing and subject to multiple interpretations. Floods wash away curves. The shoreline lines rotate. Man-made channels change their trajectories. Then there is the question of where the river begins. Does it start at the headwaters of the largest water channel "source stream"? Or is it the "farthest source", the birthplace of the farthest tributary? It is equally controversial to determine where the river ends. Many geographers believe that it is where the main stream meets the estuary. But others say that it is where the longest branch ends. Any deviation in measurement, or any change in the course of a river, whether normal or abnormal, can lead to different lengths and rearrangement. In 1846, according to the Atlas of Useful Knowledge Maps, the Amazon River was the longest river in the world, at 3,200 miles; the Nile River was 2,750 miles long. More recently, Brazilian researchers claimed that the Amazon River is more than 1,000 miles longer and 87 miles longer than the Nile. Or maybe, according to the U.S. Geological Survey, 132 miles shorter than the Nile.

Search for the source of the Amazon

A decade ago, neuroscientist James Kontos wanted change. Exhausted by his career, he hoped to pursue his passion: kayaking. Because he knew that Peru had some of the world's best rivers, he looked at maps of the Andes when something strange caught his eye. For centuries, people believed that the source of the Amazon was the Marañón River in northern Peru. The explorers then claimed that following another distant tributary, the Aprimac River, leads further upstream. In 1971, American explorer Lauren McIntyre led an expedition that traced the river to a distant stream in the Andes and culminated in the headwaters of the Amazon. But looking at the maps, Contos focused on a third, wealthy river, the Mantaro River, which seemed to meander farther than the Aburimac. So go with GPS, travel books and kayaking to see if the maps are correct. Contos has had an experience in an inhospitable environment of dry, cold, and fluffy mountain air that could not be more different from the low, flat and hot Amazon basin. After days of hiking, Contos found a new source beyond any other: a modest spring near the base of a mountain. His research was published in 2014 in the scientific journal Arria. "I thought I had made a big discovery, and it would be big news," he said. But other researchers immediately tried to discredit him. One geographer described the discovery to National Geographic magazine as a "sticking point." A dam has been built along the Mantaro River that diverts enough water during the dry season to empty the riverbed. Some scholars have argued that this would exclude him from consideration as a source. Others countered that this should not matter because the seasonality of the river is caused by human intervention. The argument began to sound like the controversy of another river: the one that surrounds the source of the Nile. There, the controversy goes back centuries. In the mid-fifties, at the height of the global exploration craze, when fame and fortune depended on bold advertising, an explorer named Jack Speck made one of the biggest discoveries. In 1858, he claimed to have discovered the source of the river: Lake Victoria. The declaration has been debated ever since, and today three separate states – Uganda, Burundi and Rwanda – claim that the source of the Nile belongs to them. But the controversy subsides as the Nile winds its way north, flowing into Egypt and then into the Mediterranean. In the case of the Amazon, it was not that simple.

"Print the Legend"

The Amazon waters travel thousands of miles before reaching the island of Marago, half the size of Portugal, which lies between the river and the Atlantic Ocean. Most of the Amazon flows north, and is the shortest route to the sea. But some head south, beginning a long, twisting path toward the Atlantic. Most people consider the Northern Stream to be the last word of the Amazon. But not Paolo Roberto Martini, 76. To prove his point, the long-haired scientist mapped last Monday morning at the Brazilian Institute for National Spatial Research in the state of São Paulo. In the final count, Amazon narrowly came out on top: 4,344 miles versus 4,257 miles. The headlines announced that the Amazon is the longest river in the world. But the victory was fleeting. Other scientists criticized the decision to use the Braves Canal. Some claimed that Brazilian researchers were looking for any way to make their river appear longer. "Manipulating measurements in order to get to first place," one remote sensing scientist pointed out.