I have to go with the natural groth of the scum from up river. I was at Mayfiel lake last week and watched this nasty stuff bubble up from the shallows in small sheets then float float off with the current. I talk to the people on the smart side of town WDF??? and they explained that as the water warms uo the algea ferments on the bottom and floats to the top. Still keeps getting worse every year and that can be atributed to the greater amount of fertalizers finding there way to the rivers.