I met a guy who used to go down to the Caribbean every April.
At the end of the tourist season. He would bring his scuba gear and underwater metal detector.
He would swim along the beach in 3-5’ of water with his under water metal detector. He claimed that he would find enough jewelry to finance his vacation. He stated that many people metal detect on the beach, but everything he found was in shallow water within 40’ of the beach. Mostly rings and gold chains.
I used to do some underwater detecting at the beach. Didn’t find enough to pay for my vacation but it was fun finding a few things.
I still have my underwater detector but haven’t been diving in many years.