Chinavasion has released a cool waterproof bluetooth speaker which has the similarity with our wireless floating speakers and aqua sounder from the past.
It seems you can use this waterproof bluetooth speaker in the sea water / salt water without breaking the speaker.
But using Bluetooth technology to stream the music is probably a bad idea. The main reason is the range between the speaker and your bluetooth cell phone/iPhone must maintain in a close distant or the speaker won’t tune the music well. And who would like to bring their cell phone/iPhone to the Sea anyway? 
But this Waterproof bluetooth speaker might works well with pool/bathtub environment.
(Price: $40 at Chinavasion)
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