We do clean lots of water every day in this country. Most towns have their own sewage treatment plants. All kinds of stuff—oils, metals, trash, etc are cleaned in these plants. It is possible to clean swimming pools. It happens every day in hundreds of thousands of pools across the country.
But, to coin a phrase, all that treated water is but a drop in the Gulf. It’s the size of the Gulf that is the problem—along with a host of other problems like wind, currents, and on and on. Nature will eventually deal with the oil in one way or another. Humans maybe will deal with a percent of it, it that—in the near term. Over the centuries, we may deal with a lot more of it. Mostly, though, the wind and the water and living things will take care of it. Oil eating bacteria and perhaps some oil tolerant vegetation and maybe some oil tolerant fauna, yet to evolve, might deal with it. But humans will only be a small part of that process, I think.
Are we protecting a few, small estuaries? Maybe. That kind of thing I think we can do and it will mean something. I think genetic engineering has a better chance of working on this problem, but I worry about the “I know an old lady who swallowed a fly” syndrome. Each solution to the prior problem creates an even bigger problem. In the end, the old lady dies.