Hydroelectric power is climate friendly, but it remains a disputed energy source. It's not always the case that renewable energy has a positive impact on the environment, as some major dam projects have proven.
Humans have used water-generated energy sources for over 2,000 years. Today, power produced from water accounts for 15 percent of worldwide electricity production - more than nuclear energy. Other renewable forms of energy, such as wind and solar, account for just 4 percent.
Water's potential, however, is far from exhausted, and it is an attractive alternative to energies that contribute to carbon dioxide levels.
Studies show that hydroelectric power could meet nearly all of the planet's energy needs. But that is not likely to happen.
"The cost-benefit ratio just does not work out," according to Andre Böhling of Greenpeace Germany. "Water as a renewable energy has to be considered in a differentiated way - on a case-by-case basis."
The varying outcomes of large-scale dam projects illustrate Böhling's point.
Old dam, new energy
Harvesting power from water has a long tradition
One such project in Honduras called the Esperanza Hydroelectric Facility offers an example of how water can be used ideally and effectively. The facility draws on existing dam structures, occupies a minimal amount of space, and the positive effects of its constant energy production are apparent.
Canadian entrepreneur Ron Turner heads the project which has been nominated for the World Clean Energy Award. The facility is the first project in the world to sell its carbon offsets in accordance with the 1997 Kyoto Protocol.
But many big dam projects develop into ecological, economic and social disasters, becoming far too intrusive on nature and society.
The Indian Sardar Sarovar Dam and the Three Gorges Dam in China symbolize environmental destruction and disregard for human rights rather than environmental progress.
Dams that result in the flooding of forest areas are especially problematic. Over the course of years, the rotting plants they leave behind release large quantities of methane - a gas that has an even worse impact on the climate than carbon dioxide.
Despite their questionable record, large-scale dams continue to be built in India, China and South America.
Discussions at an end
In much of the West, such projects are no longer conceivable.
"The discussion about big new projects in Germany is over," said Harald Uphoff of Germany's National Association of Hydroelectric Plants.
The growth opportunities that remain will likely come by way of new methods and technology. Experts are currently testing special buoys that can be hung in rivers with little ecological impact.
Another priority is modernizing the often more than 50-year-old plants in order to generate more electricity, and the project in Honduras offered one example of how that can work.
Potential for Germany?
Accounting for 3.5 percent of Germany's electricity output, hydroelectric power is the country's second biggest form of renewable energy after wind. But the economic and ecological sense of creating more water power facilities is a divisive issue.
"In the long term, people should not expect significant increases in water power production," said Andre Böhling.
Others disagree, like Uphoff, who argues that "such attitudes lead to a self-fulfilling prophecy."
Representatives from the hydroelectric power industry argue that water could provide at least a third more electricity in Germany. Their hopes lie largely with miniature plants - small, decentralized facilities with outputs up to five megawatts. They currently are responsible for 20 percent of Germany's hydropower.
"Such facilities are often enough to provide energy for small communities," Uphoff said.
15,000 unused sites
The federal government sponsored a 2008 study of German rivers and streams discovering 15,000 embankments and barrages not yet used for generating power. Industry representatives would like to see hydro facilities account for as much energy production as nuclear power plants, but environmental objections stand in their way.
German legislators passed a 2009 bill with incentives to produce electricity in environmentally-friendly ways. Those who equip their small-scale hydro facilities with ecologically-sound measures, like fish ladders, will receive more money for each watt they contribute to the power supply.
Author: Oliver Samson / gsw
Editor: Gregg Benzow