Not on the water, but near the White Mountains in New Hampshire is The Bluffs, an adult-only campground, which is a sister campground to Danforth Bay. It's in Freedom, NH. If you want quiet your best bet is to wait until after Labor Day or try the week of 8/18. Some towns are already starting school then. The week of 8/25 heads into Labor Day and families take advantage of the extra day if school doesn't start until after Labor Day but with more schools starting prior to that you may get lucky during the week.
