I live on a 25 acre lake with a very consistent 8' depth. From about mid June through September, the Illinois Pondweed breaks the surface in thick mats and covers almost 100% of the lake. It ends up looking like we live on a swamp or a field.

I am looking to find the best way to keep about a 1/2 acre area managed around my dock so that the weeds don't inhibit swimming and fishing.

I have a hard time finding a suitable herbicide. Sonar seems to be the best, but is not suitable for spot treating..
I have a weed razer and use a rake. Last summer I spent hour upon hours removing boatloads of the weeds, but just could not keep up.

Treating the whole lake does not seem to be an option as there are only a few other residents and they are not willing to split the cost of $8k per year.
I'd really like to find a way to stop the weeds before they even have a chance to make it to the surface.

I appreciate any help or shared experiences.
Thank You,
Dan K