Rivers and waterways are things that belong to all of us – no-one owns the water and we should be able to use rivers, lakes and canals in common, with just the same sort of mutual consideration that we apply with footpaths.
Currently, the legal situation (as far as I've been able to underatand it) seems confused, with some rivers accessible because they belong to public bodies (e.g. the Environmant Agency – though one has to pay a fee!) but with landowners trying to stop people using other waterways, by appealing to their "riparian rights", which I understand grew up piecemeal during the late 19th Century (access to waterways having been free before that time).
Incidentally, I do understand that some very popular waterways which are currently restricted by requiring a special registration and fee (for example the Backs in Cambridge) may need to retain those restrictions simply to avoid overcrowding. However these ad hoc exceptions should be kept to a minimum, and in general across the country there is no propspect of overcrowding or any harm or damage whatsoever from canoes and kayaks on our waterways!
If we're even moderately serious about civil liberties and equal access to the good things that our country gives us for free, I think granting a general right to roam on England's waterways in appropriate craft is a no-brainer.