It is In Bounds in the Pro Grandmaster division.. :)
In the Open division, let's see: who threw it? who is in the group?
Out-of-Bounds lines are determined, not by the PDGA Rules of Play but by the Tournament Director. Assuming that body of water is Out-of-Bounds (again, as ruled by the TD, not the Rules. Water is not automatically OB.) then the question is where the OB line rests.
In the picture we see water, we see land and we see the muddy, sloppy transitional area. If the TD declared the water OB, then it looks to me that the disc (or at least part of it) is in the muddy area. All of the disc must be OB for it to be ruled OB.
I would say that unless you can find a continuous strip of land back to shore then it is completely surrounded by water and indeed OB. In the picture I don't see such a strip of land so therefore it is OB. Loose debris does not count as land.
As of this year the rule on OB is that if any part of the disc is touching the "line" the disc is considered OB. In this case I would say that the disc is OB on the fact it is in contact with water. I would say that the "line" is were the water starts and stays in contact with the pond.