Canada home to many of the world's last free-flowing rivers Caroline Floyd samedi, 11 mai 2019 à 09:59 - Only a third of the world's longest rivers still flow freely. Water is fundamental to life on Earth and throughout most of our history humankind has been devising new ways to make it work for us. We haven't always had the well-being of the water in mind, however, and it shows. Only about one-third of the world's longest rivers are still considered free-flowing, meaning they haven't been dammed or otherwise impacted by human activity, according to a new study led by researchers at McGill University and the World Wildlife Fund Canada (WWF-Canada).