If you get sterling silver or gold you'll be fine. Avoid anything is 'plated', as this will come off really quickly in salt water. I have a cheap little ring that was gold plated and silver. The gold part is now obviously copper - and the silver is still silver. I almost always wear my 'dive' necklace (all silver stuff) in the ocean - it's under a rash guard or wetsuit so it's not flashing or getting caught on stuff. It's held up well - no tarnishing. The stuff that tarnishes is the jewelry that sits in a jewelry box.