It is argued by some that navigation of Inland rivers in England requires an Act of Parliament - A Navigation Act. Navigation acts mostly date back to the the period of the industrial revolution (The earliest from the 16th C concern the rivers Lea and Thames).
However if there is evidence of river Navigation can be found which either pre-dates a Navigation act, or is for a river for which there is no Navigation act, then where does the right to Navigate come from?
It must come from a historical and public right.
For example, take the River Monnow in South Wales. In 2003 a dig at the site of the castle at Skenfrith
found evidence of a wharf probably dating back to the re-construction of the castle around 1220. No Navigation act exists coverng this section of the Monnow.
Another example is Beverley in Yorkshire - again there is evidence for a Wharf at Beverley which pre-dates any Navigation Act which may have applied to that water.
In the Cairngorm Sailing School Case appeal, the river Spey was found to be navigable as prior to 1782 the river had been used for the transport of timber rafts, and thus a public right of navigation was acquired through long user (One of the means by which a right can be established)