Just to add one in on this Dave. The hotel has a paved area where you can swim from. There is also a beach with a café a short walk on the Lungomare from the hotel. Turn left on the path out of the hotel, down some steps onto the Lungomare and continue left. In case you don't know beaches in Croatia are very pebbly/rocky so I would recommend plastic beach shoes. If you decide to go on the optional boat trip (highly recommended) there is a beach and safe swimming on the first island you go to, and you would certainly have time for a swim there. The boat also goes to Cres, and stops at a nice beach there. The beaches on the islands are still pebbly, but not so rocky as the mainland. I hope that helps.
The hotel has a small outdoor pool (more of a large plunge pool I guess), and a larger indoor pool too.
As Mildred says pack for all weathers. I don't swim, but I do paddle 🙂 , and it was certainly warm enough for that in the middle of September.
If I can help with any more questions on the trip I am more than happy to help if I can.