Yes I have seen the same occerence here in Ohio. I have a pond that the spillway corroded & drained the pond 4-5 yr. ago. I recntly repaired the spillway & refilled the pond. There were grasses & weeds that had grown up on the banks fron the low water levels from the last few years. When I got it back up to the level I wanted all the grasses & weeds were underwater. Within 3wks the water that had always been a greenish color turned nearly total black.
