There's a great source of energy surrounding Manhattan that until recently has gone untapped: the water.

The rivers surrounding Manhattan could make a big difference for an area that's going green.

In December 2006, Virginia-based Verdent Power lowered two giant turbines into the water near Roosevelt Island Bridge. The 16-foot rotators are used to spin with the ebb and flow of the tides, and the underwater cables carry the current to shore where they connect to a small control center -- and become usable electricity.

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