Not as a hobby. Article 37 of Croatia's heritage law bans using a metal detector anywhere in the country, underwater included, to look for archaeological finds without Ministry approval, and there is no permit a holidaymaker or hobby detectorist can apply for.
Breaking it is a criminal matter, not a fine on the beach.
The rule is Article 37 of the Law on the Protection and Preservation of Cultural Goods (Zakon o zaštiti i očuvanju kulturnih dobara). It has three paragraphs:
The law has no permit for private people. The one exception is approved research.
The ban is written around purpose. It names searching for archaeological finds, and a search for a ring you dropped yesterday is not what it names. That is as far as anyone can honestly go.
It does not make such a search allowed. There is no permit to show, and it is the person holding the detector who would have to explain what they were doing, on a coast where much of the shore and seabed is registered archaeological ground. Underwater is the riskiest place of all. We found no case of anyone prosecuted for looking for a lost ring, which only means we found none.
Do not ask anyone to come with a detector. You would be asking a stranger to risk a criminal case for your ring.
What you can do: look yourself, by eye, and with a mask in shallow water. Tell the hotel reception, the beach bar and the lifeguards, describe the ring and leave your number. An honest finder usually hands things in exactly there. And if you see something old in the sand, leave it where it is.
This is not legal advice, and laws change. The official text is the law itself, in its current version on zakon.hr, and the authority is Croatia's Ministry of Culture and Media.
Kenny built Retrievly. He has snorkelled the Danube for years and keeps bringing up things that belong to other people: wallets with the ID still in them, phones, keys. That is where Retrievly came from.
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