There was a time not so long ago in a place far far away, (Newport,RI) when Floating Docks, sometimes called
Mooring Floats had to be registered as boats....with numbers, stickers and all. Even a swim raft would qualify under some circumstances.
Mooring floats have become popular in small harbors where swinging space for anchored or moored boats is tight. A mooring float is nothing more than a floating dock permanently moored away from shore and having two or more boats "tied up" on either side of the float. .... OMG: A RAFT. The idea being to accommodate multiple boats in a tighter space than would otherwise be possible. As often as not, depending on location, the mooring float is moored at both ends to prevent swinging. Camden, ME has done this for years.
I always like to look at the bright side:

It might be cheaper to REGISTER your floating dock as a boat, than have to pay Real Estate Taxes on it.

NB
OH My: I just got a brain cramp: An annual
Rafting Permit STICKER for Braun Bay.