Wind passing over open water creates ocean waves and is also a form of renewable energy. Any surfer can tell you of the power of waves and now there are technologies available to harness that power and convert it into energy supplies; for example the oscillating water column, which is sort of like a wind mill in the ocean.
There are negative environmental impacts associated with systems that harness wave energy (like impacts to marine habitat and reductions in wave height and others) but with mitigating projects and U.S tax incentives wave energy may become an affordable clean energy supply in the near future.
