I have a 20 acre pond that we flood (8-10" deep) via well during hunting season but is dry most of the summer. There's always a healthy stand of barnyard grass but I always spray a couple acre kill hole in front of the pits. For some reason this entire duck season the bottom was COVERED in moss/algae and would make it's way to the surface at times. Decoys and decoy lines were an absolute nightmare. We have never had this issue before. We had a nearby creek come out of it's banks and flood us (flowing water) for about 3 weeks in March. Could that have brought something in that caused it? I think I see a ton of copper sulfate in my future.