Northern Highland American Legion State Forest in the Boulder Junction area has a network of water side campsites that get very little use. There are lake and river sites and most are connected by waterways or in some cases portages.
And it's all free though a vehicle park sticker may be required. I'm only familiar with a few of the campsites and portages but they always looked nice and though I've wanted to put together a trip using some of them I never get around to it.