They are installing an underwater turbine downstream from a hydroelectric power plant in the Mississippi River near Hastings, Minnesota. The turbine was made by Hydro Green Energy from Houston, Texas -- Verdant Power is another manufacturer. They expect to increase the plant's output by 5%.

"We don't require that massive dam construction, we're just using the natural flow of the stream," said Mark Stover, a vice president at Hydro Green Energy, the Houston-based company leading the project. "It's underwater windpower if you will, but we have 840 or 850 times the energy density of wind."

Hydrokinetic turbines like those produced by Hydro Green and Verdant capture the mechanical energy of the water's flow and turn it into energy, without need for a dam. The problem for companies like Hydro Green is that their relatively low-impact turbines are forced into the same regulatory bucket as huge hydroelectric dams. The regulatory hurdles have made it difficult to actually get water flowing through projects.