Dear Jörg! Good question! I can not think of any appropriate solution of this problem. I can only think of one removal of a dam in US, which is the best solution so far. Sorry, I can remember the river. Anyhow, an appropriate solution is mainly a question of dimesion. Would be a good topic for a conference. All best Georg

As mitigation measure to such activities that can negatively effect the populations of certain aquatic species, special conservation practices including management and reintroduction of the species at both upstream and downstream have been observed.

We have a fantastic example of failure in a Queensland river. They built a fish elevator to transport fish up and down the dam wall. Cost millions. But it only works when the dam is full! In Australia that t rarely ever occurs.

John D. Koehn, Mark Lintermans (2012) A strategy to rehabilitate fishes of the

Murray-Darling Basin, south-eastern Australia. Endangered Species Research 16: 165–181, doi: 10.3354/esr00398

This paper should be a good starting point for chasing down the relevant information on the largest attempted fish passage remediation program in south eastern Australia.

Georg,

That would be the Elwah River on the Olympic Peninsula of Washington State.

There are dams on streams with few or no fish! Think of small irrigation dams on Mediterranean islands. In many cases the only species surviving in the upland portions of these streams are the European Eel. I have knowledge of eels actually finding refuge in small dams with slanted spillways on Cyprus (they enter and survive in the dam, e.g. Livadi Dam, Pomos area). But evidence of this is scarce. Although the small river is degraded from water abstraction impact the dam may function as a refuge only when aquatic habitat-continuity to the sea enables eels to successfully migrate up-stream - all the way up the spill-way.