I like swimming in the sea. I'm not a good swimmer at all, but I do like it. I took swimming lessons when I went to University at 27 in order that I might improve from just being able to save myself from a canal to swimming for fun and health. I am told that it is a very good exercise for asthmatics, and, if I were able to endure the tedium of plodding up & down a swimming pool, it would be great for my breathing and my rather underdeveloped upper body strength (at least in comparison with my legs).
I do struggle with cold water. I don't feel the cold as much as most people, and I have fairly cold showers, but entering cold water can quickly give me an asthma attack, which makes me less inclined to do so.
I've also tended to worry about all my stuff being nicked while I'm in the water. Overly so, maybe, but I rode alone, and being isolated without my kit would be a concern.
Thirdly, I've not enjoyed swimming because of my size and body image, ever since I took a lot of steroids when a teenager. They kept me alive, but they did make me put on a lot of weight very quickly at a very sensitive time.
That said, we went for a lovely ride with the Clarion last year, down past Ford in Sussex, and we had a swim in the sea then. It was brilliant.