LSP has used a combination of chemical and harvesting. They did a very good job this passed summer.
FYI
From the LSP Newsletter June 09
"The marina was treated yesterday for MILFOIL. Hopefully It will begin to die off in the next few weeks. In mid July we will hire a diving firm to start hand pulling the remainder of the weed. We have entered into a 5 year plan with the State and Town of Gilford to eradicate up to 80% of MILFOIL in our Marina. We also obtained a grant from the Gilford Conservation Commission to help us with the cost. Next year we hope to obtain a State grant for additional work."
Sad to say, it needs to be a yearly event. Milfoil is very stubborn.