Water power was the engine of industrialization and Germany's most important source of energy at the beginning of the last century: there were more than 100,000 hydro-electric power plants back then. Today, only around 7,500 of those are left and they deliver roughly three percent of German power.

Experts estimate that the share of water power could rise up to 50 percent if roughly 20,000 older and smaller hydro-electric power plants were put into operation again.

Environmental protection vs. water power?

But reinvigorating water power's potential is highly contested in Germany. Voicing concerns about the protection of fish populations in rivers, many water authorities, fishermen and environmentalists demand that as few dams as possible should be built for power purposes.

The resettlement of migratory fish is only possible if stream courses are renaturalized, environmentalists claim. That's also what a European Union water directive stipulates. It states that by 2015, all creeks and rivers must be made passable for all creatures. Part of this measure also covers the restoration of flooding areas and riparian forests adjacent to bodies of water, which are important spawning areas.

Migratory fish like sea trout and salmon hatch in the upper course of a river and then grow up in the sea. When they are sexually mature, they migrate back to the river to spawn.

The eel is a highly endangered migratory fish, according to the Convention on International Trade in Endangered Species of Wild Fauna and Flora. It has a converse life cycle: hatching and spawning in the Atlantic, it spends almost its entire life in the river and has to return to the sea to procreate.

Water power proponents counter that 100 years ago, the fish population in German bodies of water was ten times the size it is today - despite a ten-fold water power usage at that time. They see pesticides and fertilizers from agriculture, chemicals and drug traces in the water as the main threat to fish. Fishermen in turn say that water quality has improved over the last decades, but that resettlement is a long, protracted process.

Using available resources for energy turnaround

Climate protection activists call for a paradigm change and for assessment of competing environmental interests. "Many small-scale dams have been here for centuries, and they should be used for power production for the energy turnaround if at all possible," Rolf Ahlers, of Friends of the Earth Germany (BUND), told DW. "We have to push climate protection forward, because without climate protection, there can be no nature conservation."

Axel Berg, head of Eurosolar, the European Association for Renewable Energy, takes a critical view of fishing associations, claiming that they impede the use of hydro-electric power plants with impertinent arguments. "River fishermen try to tell us that hatchery fish they release into the wild are really ecological. But they're only trying to save their hobby, and we can't afford that, because the climate's in danger," Berg said.

He wants to expand hydropower in Germany, but in harmony with nature. "Eighty to 90 percent of the fish in our rivers are captive-bred fish and not native. They are released in the wild by fishermen in the springtime, fished out again in the fall, and then land in the frying pan," Berg told DW.

Berg also believes that costly "fish ladders" or "fish passes" set up next to dams to facilitate fish migration are not necessary in every river. Instead, they make sense only where migratory fish still actually exist, according to Berg.

Producing power independent of sun and wind

Proponents of hydro-electric power plants admit that wind and solar power will remain Germany's most important and cheapest forms of renewable energy in the future. But they still think adding more water power to the mix makes sense since hydro-electric power plants produce power mostly in winter - they work when the sun doesn't shine and the wind doesn't blow. In addition, water power can be easily "stored" and is then ready when needed. "That's convenient," Harald Uphoff, director of the Federal Association of German Hydro-Electric Power Plants, told DW. "It's an elegant addition to photovoltaics and wind."

Yet costs for generating power from water vary greatly. The larger the mass of water and the steeper the downward slope it travels, the lower the cost, Martin Weißmann, lecturer for water technology at the University of Applied Sciences in Karlsruhe, explained. Large hydro-electric power plants in Europe produce one kilowatt hour of electricity for three to five euro cents, medium-sized plants (2,000 to 3,000 kW) for roughly ten cents, and plants at small bodies of water for up to 20 cents.

Even though power from these small hydro-electric power plants is expensive, Uphoff still believes they are important. They are a good addition to the decentralized, environmentally-friendly power supply, and save costs in the expansion of power cable networks and in the contested resettlement of entire villages. He sees smaller plants as especially interesting for regions that don't yet have power: "Just one small waterwork can reliably supply two or three villages with power for a whole year."