It depends which rivers. Up here in the midlands, the Canal and River Trust issues licences for some rivers, but not all. Their list includes parts of the Severn and parts of the Avon.
Rivers Only Licence covers the following:
Avon (Hanham Lock to Bath)
Bow Back Rivers
Fossdyke & Witham (Torksey to Boston)
Lee Navigation (Hertford to Limehouse)
Ouse and Ure (Goole to Ripon)
Severn (Stourport to Gloucester)
Soar Navigation (Trent Junction to Leicester)
Tees (Tees Barrage to Low Worsal)
Trent (Shardlow-Gainsborough, including the Nottingham & Beeston Canal)
Weaver Navigation (Winsford Bridge to Manchester Ship Canal)
Down your way there is the Avon Navigation Trust:
Avon Navigation Trust | Home
Google is your friend.