(As sent to me, but unfortunately not personally experienced.)
We had a beautiful day for our hike, with highs in the 80's and lots of sunshine. The water was not warm, but also not cold enough to set off alarms by the thermal indicators. Two people got in a good long swim, and others of us at least had an invigorating dip before or after lunch.
Several of us had other engagements that kept the day shorter than we would have liked -- probably only 4 miles or so roundtrip. But others went further and did perhaps 9 miles roundtrip.
All in all, a good day to start the summer season.