Today I noticed that the grasses that usually grow on the house side of the pond were gone. Maybe the grass seeds and then dies. And I noticed that on the woods side of the pond that there was an oily sheen that collect debris and touched the shore. I also noticed that there seems to be fewer tadpoles and a lack of frogs. I heard them with their plucked banjo call, but I didn't see any mature frogs at all. I wonder where the oil came from. What can I do about it?