These are not meant for getting seriously wet.  Do not go in the ocean with them.  Otherwise, they handle sweat and normal wet conditions fine, and are super comfortable after the break in.  Get the rubber ones for going into water.

Update: Two years in, and these are starting to stink.  I keep scrubbing them with soapy water, and they are wearing down faster than I had hoped.  like the hemp is not as thick as I hoped.