Not a particularly comforting piece of news for the stretch upriver that's been saturated in crude, but from a bigger perspective, to contain the disaster to only that 25 mile stretch is significant. The health of the entire river, and connecting bodies of water--especially Lake Michigan--depends on it. Preserving other parts of the river will most likely help in the eventual recovery of the contaminated stretch. Wildlife and fish have some immediate places to escape to, and, in the long run, can eventually re-colonize the recovered portion of the river.
I'm skeptical that they can stop every ounce of oil, whether sheen or the thicker stuff, from making it's way downstream, but stopping the major flow means a lot to the health of the river, and us.
It makes me think of the expression, "everybody lives downstream". Indeed, we're just downstream, and thank God they know that upstream.