Going somewhere exotic? Discuss in here..
My guess is that they are concerned that other people would use the water sports people to argue that all beachgoers can go to the beach, and then others argue for their group etc.
In Fuerteventura, the police called the water sports people off the water, photographed them and said that if they did it again they would be fined or jailed. They may not give people that grace when they are sure the word has got about.