UNDERWATER WEDDINGS

While this might be a bit unconventional, it is something that I have some experience in doing.  We also operate the largest scuba diving operation on the island, St. Croix Ultimate Bluewater Adventures (SCUBA).
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Back in 2003 we helped put together an underwater wedding that set a Guiness World Record for the largest ever held. (We had 106 divers underwater at the same time--only one couple were getting married).
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Typically the vows are printed out on laminated sheets and I run my finger along the text just as if I were reading it.  The couple then each runs their finger along the text also as if they were reading it aloud.
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While this doesn't require that the participants are certified scuba divers it certainly helps.  If there's someone in your wedding party who is not they can participate in a Discover Scuba Diving experience and attend the wedding.
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Check out this video that was shot for a Travel Channel story on underwater weddings.