Gravitational Vortex Micro-Hydro Generator is Fish Friendly
An Australian engineer by the name of Franz Zotlöterer inadvertently discovered an efficient way to harness water power in his quest to aerate and improve water quality. It seems that by diverting a bit of a stream into a circular basin, with as little as 0.7 meters of drop, you can produce power with up to 80% efficiency. The prototype is larger and somewhat less efficient, but it does demonstrate that it works with relatively low turbine speeds which will aerate the water well and is safe for fish swimming upstream. This seems to be an excellent alternative to standard micro-hydro generators which generally require larger drops to be efficient (the patent is already in the mail).