>> ann thompson is nbc's chief environmental affairs correspondent live in venice, louisiana, and she's moving, that's right, she's on a boat this morning. so ann, as you go along in the oil-free waters there, what's the caveat here? the administration is out thing the fact that three quarters of the oil is gone but nobody know what is the impact is. >> reporter: right. you still have the 26% that is in the water, and it is 26% of the very large spill. that's over 1 million barrels of oil that are still basically unaccounted for. think of it as four exxon valdez spills that they cannot find yet. they think most of the oil that's there has been weathered, but it is certainly a huge caveat here because there are all kinds of questions about just what this oil and those disper sants dispersants are done to the environment. what has it done to the next