Up north inBC sonata not the issue. It really does have more to do with the minimal tidal exchange I think. I went swimming in Desolation Sound in June and it was delightfully, 'stay in the water for an hour' warm!

BUT----

4' below the surface was quite chilly! Treading water got your feet cold while floating on your back was delightful. Quite definitely a shallow, but warm, layer of water.