Hey Mr Bonk,
The police hate Jet Skiers almost as much as the rest of the community and as such take great pleasure in busting them for inappropriate and reckless behaviour. All you need to do is take down their rego numbers off the side of their ski and then ring the local water police. They are used to these calls.
The water police are usually only 20-30 minutes away and usually rock up with a fresh citation book and a stern attitude. I've done this before when Jet Skis have been slaloming in between students and swimmers outside of their allocated area.
Traveling at 50 knots 30 feet from the waters edge in a family swimming zone is ridiculous, irresponsible and highly illegal. You would be doing the community a service. I don't hate all jet skiers, just the ones who act foolishly and give the others a bad name.
Good winds,