The limit is being enforced using hi-tech speed cameras

The Lake District National Park Authority (LDNPA) introduced the byelaw on Windermere, Cumbria, in March.

The authority said this has led to a safer and more tranquil environment.

However, it has also meant fewer high speed vessels have registered to use the lake, leading to an estimated £60,000 drop in revenue.

'Striking' improvement

And a number of lake users are currently facing possible court prosecutions for exceeding the speed limit.

Emma Dewhurst, LDNPA corporate communications director, said: "The difference and improvement in quality of enjoyment is more striking than we could ever have hoped for.

"Local people and visitors are constantly telling us how much more they are enjoying the lake. And lake users, including sailors, canoeists, people who fish, row, swim or paddle, have got a bigger lake back."