Hi!
I just saw this; it's about a relatively-novel way to use currents and other slow water flows to generate electricity. Click on the picture to read about it:
I do wonder about the maintenance costs and overall cost-effectiveness. I'll bet an installation like this would be encrusted with barnacles, algae and other sea life very quickly, so the maintenance costs will not be anything like zero. Have you ever seen a picture of what the undersea parts of drilling platforms look like after a few years? See below. All of that aside, it's still fun to think about. Who knows, maybe it'd work? You can click below for an article on drilling platforms as artificial reefs:
Cheers! generalist