To be honest, we really didn’t mess around with swimming too much. I think you can swim at the beaches in the summer without much problem. The winter it is probably too cold for more than a quick dip polar bear plunge-style.
We did go swimming in between the divide in the continental plates in the run off water from the glacier there. That was amazing! Had to do it in a dry suit as it was freezing cold, but it was really cool and the water was more than crystal clear.