By Macarena Soler
Seen from space, the Earth is mostly blue. It is estimated that close to 70 percent of the surface is covered by water, and the oceans contain a little more than 96 percent of all the water on the planet. Just 3 percent of the water on the globe is fresh water, and part of that is found in rivers, which are essential and irreplaceable for maintaining terrestrial and marine ecosystems.