The Environment Agency has won a High Court appeal over boat registrations on the non-tidal Thames.
At a hearing in December boat owners from two marinas - Thames and Kennet at Reading and Penton Hook near Chertsey - had argued their vessels did not need EA licences because they were off the main river.
Now two High Court judges have ruled that boats on marinas connected to the Thames must obtain annual licences.
Waterways Manager Barry Russell said: " This is the outcome we were hoping for, as we have always been confident that our position on the points of law considered in this judgement is the correct one.
"As we made clear to the boating community in 2014, we obtained the opinion of an eminent Queen’s Counsel on the argument by some boat owners that the marinas were not part of the River Thames, and had received his advice that they were.
"We then reminded boat owners of the obligation to register boats kept in marinas, but a number chose to ignore our advice. Some of those are the subject of the prosecutions which gave rise to this High Court judgement. The same Queen’s Counsel who gave the advice on which we acted, represented the Environment Agency in the successful High Court proceedings.
"We now intend to carry on with the arrangements that have been in place since we implemented the Inland Waterways Order in 2011."
In a letter to boating organisations Mr Russell said: " Another important feature of this case is the measured approach we have taken throughout. We have scrupulously assessed the merits and risks of each step to ensure we were at all times acting in the best interests of the wider River Thames boating community and the tax-paying public.
These principles have always underpinned our enforcement of navigation legislation on the waterways we manage, and always will."
Legal action against unlicensed boats in marinas had been suspended awaiting the legal judgement. Mr Russell said he could make any further comment - due to 22 potential prosecutions before the courts again.
Boaters who appealled have yet to comment.
Link to earlier High Court story.
Story dated March 27th 2017