Pond cleared of weeds

We developed the pond garden out of a triangle of swamp about 20 years ago, and planted out between 450-500 trees around it. It is a favourite part of the grounds for us. We are constantly fighting to keep it reasonably clear of pond weeds and couch grass - no one told me couch grass would thrive in three feet or so of water! I like to use the pond as a mirror in my photography, so that's the driver to keep it relatively clear!