I have studied upon the watermeal question and found it to be a real possibility. I will have to go back to the pond to conduct a more detailed inspection. The problem I have with this option is the watershed/pond isn't very fertile and from what I have found it appears that both duckweed and watermeal seem to prefer nutrient rich ponds. My pond does, however, meet the requirement of still water as it is surrounded by trees. Will this stuff die off when it gets cold?