Our weed control is multi-layered.
Our lake is kept filled by ground water from the surrounding hills, it enters the lake through a specially created reedbed that is being allowed to develop naturally. The habit captures the silt from the ground water and the new habitat feeds on the incoming nutrients which reduces the ability of weeds to grow.
The lake itself is protected by high TEC ultrasonics which destroys algae etc at cell level as it forms.
Of course the swans and ducks eat any weed that gets past all the other defences.
Thanks for suggesting grass carp, that's now first reserve!