Swimming is great exercise but it can get a bit boring. Have you tried mastering a surf board, and riding the waves?
See http://www.surfing-waves.com/surfing_lesson_one.htm
It it all sounds a bit too energetic but you like the general scene, maybe you should take an interest in the life saving aspects, and be a beach lifeguard or patrol your local beach. Surf Life Saving Great Britain reckon they have been responsible for saving 20,000 lives in the last 50 years
http://www.surflifesaving.org.uk/extra.asp?id=5384&OrgID=1309
