4. Dammed if you do...

Rivers Must Flow

Rivers act as the planet's circulatory system. Like our body's circulation system, the planetary one doesn't work very well when it's clogged. If a river's flow is its heartbeat, then we humans are the heart disease. We've blocked most major rivers with dams, bled them dry with water diversions, and given up all too many once-great rivers for dead once we've used them up.

More than 50,000 large dams now choke about two-thirds of the world's largest rivers. The consequences of this massive engineering programme have been devastating. Large dams have wiped out species; flooded huge areas of wetlands, forests and farmlands; displaced tens of millions of people, and affected close to half a billion people living downstream.

Large dams hold back not just water, but silt and nutrients that replenish farmlands and build protective wetlands and beaches. Dams change the very riverness of our waterways, in ways we can't always see, but that the earth can certainly feel.

Of all the complex and interconnected environmental disruptions that dams inflict on the landscape, the most obvious is the permanent inundation of forests, wetlands and wildlife. Reservoirs have flooded vast areas - at last count, the world's dams had flooded an area bigger than the United Kingdom.

Equally important is the quality of these lost lands: river and floodplain habitats are some of the world's most diverse ecosystems. Plants and animals that are closely adapted to valley habitats often cannot survive along the edge of a reservoir.

Dams also are usually built in remote areas that are the last refuge for species displaced by development elsewhere. In large measure due to dams, freshwater ecosystems are losing species and habitats faster than any other type of ecosystem.

Large dams also fragment the riverine ecosystem, isolating populations of species living up and downstream of the dam and cutting off migrations and other movements. Because almost all dams reduce normal flooding, they also fragment ecosystems by isolating the river from its floodplain. The elimination of the benefits provided by natural flooding may be the single most ecologically damaging impact of a dam.

Now, watch the video below, which explains why some Chileans are organizing to stop the construction of a dam in the Patagonia region of Chile. Listen as politicians make the case for building the dam. They argue that the dam is a source of clean energy which will help to wean Chile off of imported fossil fuels.