I believe the road question would depend on what road you are talking about. State roads, the right of way is usually owned by the state and is 30' or so out both ways from the center line for a typical 2 lane road. For larger state roads, in urban areas or where the road has moved this can vary larger or smaller but it is a good enough rule of thumb for rural areas. County, City and Town roads are a mishmash of ownership. Many of these only have a right of way for the road use and maintenance of it. The adjacent owner's property can go to the center line of the road. Other places the municipality owns the road bed with no shoulder, others the shoulder is included but varies in width. The locality and their wording of the original ROW taking or conveyance would govern in those instances. Safest bet would be to adhere to the posted signs unless one verifies the signs are invalid at the controlling municipality.
What greensider said about waterways is how I understand it as well with the addition of no anchoring allowed either. Long time ago I asked a DEC officer this question and he said if you can access it by boat without portaging you can float it but don't get out or anchor as the underlying land and shore is private.