Only about one-third of the world’s longest rivers remain free-flowing, meaning they have not been dammed or disrupted in man-made ways, reports a new landmark study. While there are a few exceptions, like Asia’s 1,700-mile long Salween River, most of the remaining free-flowing rivers longer than about 600 miles are now restricted to remote regions of the Arctic and to the Amazon and Congo Basins.Two-thirds of the longest rivers no longer flow freely—and it's harming us

A new study warns that many of the benefits rivers provide, from water to food to flood control, are increasingly at risk thanks to dams and diversions.
By Stefan Lovgren National Geographic