Don’t look now, but oil from BP’s blown-out well is getting harder to find. ABC News reports that oil skimmers just two weeks ago were scooping up 25,000 gallons of oily water per day, but last Thursday captured only 200 gallons.

Of course, skimmers are literally only skimming the surface of an oil spill problem that still lurks deep underwater across a vast expanse of the Gulf. Consider that most of the 200-million gallons of oil, which gushed unchecked for nearly three months, never made it to the surface and when it did was bombed by more than a million gallons of toxic dispersants. In addition, the crude has been whipped apart by storms, tides and currents. Much has been eaten by microbes.

What’s left, in the mile-deep zone between source of leakage and the surface is a situation never quite faced before. As ABC concludes:

Experts stress that even though there’s less and less oil as time goes on, there’s still plenty around the spill site. And in the long term, no one knows what the impact of those hundreds of millions of gallons will be, deep in the waters of the Gulf of Mexico.