colin, could you pass this on to Robin Reynolds, as i have posted similar on a number of forums..
Fleetwood had the same problem for a number of years with many attempts to clear it without success.
Then, Wyre Borough Council who are responsible for the upkeep of the lake chanced upon a remody that others had used.
They implanted into the lake bed two sonic impulse transponders, [ one at each end of the lake], and this worked with IMMEDIATE effect, clearing the weed within about 10 days, never to return again.
we all took the preverbial at their initial response to placing these in the lake, but it were us that were left with egg on our face.
neil.