Many of those streams are not natural and those which are need to be maintained there is a complex network dams as well as constant dredging to maintain them passable to boats year round.

The main beneficiaries of the license fees in England and Wales are the British Canal Trust and the Environmental Agency both of which use the money to maintain the waterways and the environment around them.

The fees are next to nothing for smaller vessels, for unpowered boats the fee is incorporated into the membership fees for the clubs.

Rentals are exempt as they fall under the business fee of the rental provider and visitor licenses are available for short term that cost next to nothing.

As far as I can tell this is about artificial canals, not natural streams of water.