Nature has many strange things, once you try to explore the nature, then you come to know about a lot of stuff, but you only come to know, you often don’t understand the reality of the stuff. Now, scroll through this article, the divers at First, I Thought It Was An Oil Spill. When They Zoomed In? My Mind Was Blown.
At first they thought that this was a random oil spill, just as the thin film of oil sets over the surface of the sea, but to the extent of you surprise, this wasn't an oil spill. And when they tried to get closer to the oil spill (Apparent) it tried to adjust it self according to the position of the divers. Yes, it started to move.
You can see the screenshots, there the black portion is that strange thing, and the divers can be seen too, in the last slide you can see the video of the whole incident.