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Waterways licence, I think it's called. Estuaries and the sea + some rivers are exempt. Some reservoirs charge a premium (thanks Anglia Water...) or you have to join a registered club at the reservoir.
https://waterways.org.uk/waterways/using-the-waterways/canoeing-paddle-boarding
I only found out when I was warned by someone nearby that they have been asked for theirs in the last couple of weeks on the Great Ouse.
For £318, I'd hope so! Realise I also need a paddling licence for all the rivers round here...