Google “Swimming Tourism” and you’ll find extraordinarily beautiful, fascinating locations for open water swimming holidays. These adventures are with a group of other swimmers, swimming to explore beautiful coral reefs. I have not done one of these yet, but hope to someday.
I suggest you research the one that seems the most appealing to you in great detail, as to the amount of area you will be swimming per day and the required swimming skill level etc. Also, research the area so you do not find later that the pictures did not represent what the area truly looks like.
An example of a trip misrepresentation:
My husband and I had a misrepresentation of an area, on our honeymoon trip to Jamaica. The excursion adventure trip was touted as a lake in a cave. The site photos were enticingly beautiful, and it showed a boat ride on the lake. When we did the trip it was a small rowboat that they pushed off of shore about 5 feet to the middle of the body of water. The “lake” was the size of a swimming pool. Woo, were we let down, the photos made it look larger than its’ reality.