One of the most common misconceptions about America’s energy supply is that a vast majority of it comes from hydropower. It’s a nice fantasy, as it would mean a tremendous amount of reliable, clean energy, but traditional hydropower—in which an existing body of water is altered to generate energy—is not without its problems.

Dams are expensive, generally rely on dated turbine generators, and aside from interfering with local wildlife, can endanger nearby human populations. Even futuristic designs, like this Dutch energy island, require massive construction, entailing a heavy initial investment and incurred carbon debt.

But one of the fastest emerging fields of clean, renewable energy also involves the water, but with fewer of the concerns. Hydrokinetic energy works by harvesting energy from the natural, recurrent movement of water, without significantly altering the water flow or landscape.

As recognizable as wind-turbine lookalikes in the water, or as odd looking as jointed bouys on the water’s surface, hydrokinetic power generators come in many forms. But continued development will no doubt thin the heard to two or three highly efficient designs, and, as this map shows, could be a major new step both toward a cleaner energy system, and a more energy independent nation.