Question Hydro electric generation.

[SiberianTiger]

And there is a current in the oceanic water currents.

Whatever method you use to draw an energy from an ocean current, building a power plant amidst of ocean is not a good idea, because consumers mostly want their electricity delivered to them to a firm land 1000s of miles away from where strong ocean currents are found.

One way to contain ocean currents is to harness tides, as said above. There are different designs of [ame="http://en.wikipedia.org/wiki/Tidal_power_plant"]tidal power plants[/ame].

 

[PhantomCruiser]

I hate to be a billboard for the place that I work, but TVA is a great example of a hydroelectric system that work. I mix of big dams in the higher elevations and smaller dams across the Tennessee river for navigation and flood control.
Before the system of dams, the river could be crossed on foot during certain times of the year, and would be dangerous/deadly during the spring rains. Flash floods were common, with people losing their homes/crops/livestock and sometimes their lives. I don't think anyone would argue that the TVA river system has been harmfull to the environment. As a caveat, there was some arguement about a little fish called the snail darter, but that fish has not died off, and in fact has been found in several other places nearby.

 

[Urwumpe]

As a caveat, there was some arguement about a little fish called the snail darter, but that fish has not died off, and in fact has been found in several other places nearby.

Just to give you a tiny push closer to absolution ... scientists lately found out, that the oh so dangerous feeding of birds in the winter is actually badly necessary and good for the diversity... because otherwise birds would no longer find food because of the highly optimized agriculture, also it has a strange effect on evolution, making birds more adapt in eating seeds. And sing later in the morning, because happy fed birds sleep also longer.

Ecology is no linear scalar science, it is multidimensional and fractal. What appears bad in the first glance and can be terribly good on second sight - and the other way around.

I personally think though, many water management systems in the world are too tightly controlled. The old wide river beds had been Malaria nests, but at the same time, they also had been great places for farming and fishing and flood damage was much rarer then it was today. Because of the tighter control by the dams, the chain reaction if the dams go beyond design limits is much worse today, because humans started living closer to the now "tamed" rivers.