I'm not a lawyer, but I did a little research and here's what I've come up with:
328.48 Vessel registration, application, certificate, number, decal, duplicate certificate.-
...beginning omitted due to irrelevance....
(2) Each vessel operated, used, or stored on the waters of this state must be registered as a commercial vessel or recreational vessel as defined in s. 327.02, unless it is:
(a) A vessel operated, used, and stored exclusively on private lakes and ponds;
(b) A vessel owned by the United States Government;
(c) A vessel used exclusively as a ship's lifeboat; or
(d) A non-motor-powered vessel less than 16 feet in length or a non-motor-powered canoe, kayak, racing shell, or rowing scull, regardless of length.
...continuation omitted due to irrelevance...
So if you are using it on private waters only then there is no legal requirement to register it. I don't know where you are talking about, but just remember that there is a difference between truly private water and "waters of the state" that have no public access.