We have Eurasian Millfoil on our lake (Puslinch Lake) for about 30 years now. For those who don't know the plant, it is a very strong, thick weed that has the wonderful attribute of being cut by the prop, floating away only to plant itself somewhere else and continue to grow. Once a lake is infected with it, I believe you can mitigate the problem but will not be able to eliminate it entirely (sorry).
We have done several things over the years to try and control it. Weevils are one potential solution, although it didn't work for us. A weevil is a type of water based beetle that will eat a weed or two (completely - the weed dies) as it goes through it's lifecycle. So we put over 30000 bugs into our lake over 3 years (if memory serves) at which point they were supposed to be self-sustaining. Unfortunately survival rates in our lake were very low, for reasons unknown, so this option didn't work for us. The beetle's aren't cheap either - but if this works for you it is an ecologically friendly solution. What we are doing now is a combination of dredging and a chemical spray that kills the plants each year. This chemical is supposed to be "pretty safe" however I do worry that I'll be growing a third arm or something in 20 years or so. I don't recall the name of the chemical but it is very effective.
One other thing to note on this is that you want to get on top of this asap. Don't let it get out of control, especially since you say your lake is only 7' deep. As this plant dies, it creates more sediment on the lake bottom, out of which next years crop grows and the cycle continues. Before you know it you won't have a lake, you will have a swampy mud puddle. These weeds are very strong. Only a few wrapped around the prop will affect boat speed.
I recommend you reach out to the PLCA (Puslinch Lake Conversation Association) at placa.ca. Describe your situation and see if they have any experience with lake-savers.com. I suspect they will at least know about them, as they have been battling this problem for many years. If you can't reach them, PM me and I will put you in touch with someone directly. Best of luck with this - it is a nasty problem to have!