Yeah when I first noticed the oil a few months back it was all in one corner from the wind. And after a few weeks it disappeared. When I scrubbed the Christmas tree along the bottom I saw some oil film or a look alike come to the surface. Which me to believe it might have sunk down to the deeper parts of the pond. I believe the oil was from our pond builders machinery and he said he changed some oil filters a few hundred yards from the pond that could have washed. When I saw the oil it was black and thick and if I could have scooped it up it would have been no more than a gallon