Supernatant

Moving along with this interesting vocabulary challenge... Word no.4, Supernatant, floating on the surface.

Of course, it's not quite that simple... as I understand it - and this is one of the few words of the challenge that I happen to know :0) - supernatant is really quite a technical term, and generally requires something like a blood sample and a centrifuge to achieve. I think, though, that oil on water qualifies.

So here is a car park puddle with a supernatant of oil, leaves, and cherry blossom.