See if you can get it declared a no rafting zone.
But really, do what works, put the restaurant and the Gilford PD on speed dial, everytime they start up, call them both. Call them several time every night. Eventually they will get tired of you calling.
If that doesn't work consider a lawyer. It will cost you but it might be worth it. A good lawyer will tell you if you have any legal options for short money or sometimes even free for the initial consult. At least you will know if you have legal options.