I stumbled across mention of the 1904 'Godmanchester' case before the Lords while reading about the Great Ouse, here: http://en.wikipedia.org/wiki/River_Great_Ouse
citing this (Boyes & Russell 1977, pp. 149–151). It appears to suggest that the House of Lords supported the right of a stockbroker Simpson to nail shut the gates of the navigation against the claims of the Bedfordshire and Huntingdonshire County Councils that the river was a public highway. I've not time to read up on all this, but wondered if it might hold any interest for some of our more committed researchers.
(I note that Wikipedia may not be a very scholarly resource, but thought it might provide something to follow up; when I read sentences like 'the navigation was bought' presumably that alludes to the navigation rights, which can be bought and sold, as I presume a river itself cannot. Is that right?)
Hope this helps.