In summer the surface of our garden pond is covered in a thick layer of duckweed and dealing with it is a real problem. If I skim it off with a rake I inevitably catch a lot of tadpoles and newt-poles that live amongst its tangled, thread-like roots and it takes a long time to release them all and return them to the pond. But this morning I accidentally discovered a quick and simple way to remove duckweed in large quantities, at little risk to the other pond life. I was weeding out sticky Jack (aka cleavers aka goosegrass) and accidentally dropped some in the pond. When I fished it out it was covered with duckweed, entangled in the tiny hooks that cover sticky Jack - see http://beyondthehumaneye.blogspot.com/search/label/sticky%20Jack
A handful of sticky Jack did an even better job and after ten minutes of using this technique, which uses one weed to get rid of another, the pond surface was almost clear. I couldn't find any trapped tadpoles in the sticky Jack – the technique just removes the duckweed from the surface. The only problem is that now I’ve run out of sticky Jack – and I know the duckweed will return.