Mystery thing

We´ve had a sunny and warm day, perfect for a bike ride. We went to the bay. We sat there and listened to the water cluck to the beach. And suddenly a man with a jet ski appears on the sea. He drives very, very slowly and got something on tow. And there I had todays blip!
Later on we pass the marina. And there is this mystery thing. A man in a boat informs us that the thing is a pontoon to jet skis and serious jet skiers use that. We have no idea what that means, we are no water people.