Looks like an underwater phone, but no bluetooth. I think your problem is not with technology, but setting reasonable expectations for accessibility. You could let people know that you can't be reached for the next few hours when you start your swim. Alternatively, you can stop and check your phone every half hour or so, and let people know that you can't respond right away, but you'll check messages regularly.
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http://www.pcmag.com/article2/0,2817,2034585,00.asp
Looks like an underwater phone, but no bluetooth. I think your problem is not with technology, but setting reasonable expectations for accessibility. You could let people know that you can't be reached for the next few hours when you start your swim. Alternatively, you can stop and check your phone every half hour or so, and let people know that you can't respond right away, but you'll check messages regularly.