6. Rio de la Plata, Uruguay

Rio de la Plata, Uruguay [huanqiu.com]

Fresh water from the Paran and Uruguay rivers collides with sea water from the South Atlantic Ocean in the muddy estuary of Rio de la Plata. This estuary feeds surrounding rich and fertile land, also provides the natural habitant for variety of endangered species, such as the rare La Plata dolphin. Climate changes may lead to flooding of the coastal area.