Think of the best body of water in which you have ever gone swimming. Why did you like it so much? ~

It was a private lake and I didn't have to wear a suit.

Atlantic and Pacific oceans because salt water bodies are more exciting than inland fresh water bodies.

A natural pool of water beneath a double set of falls.  You could swim under the falls, the water was not too deep and the falls not too swift.  

The quarry where we used to go swim when we skipped class in high school.  The water was crystal clear and freezing but I loved it.  To this day my mother knows nothing about those fun days of yore.

Nothing better than floating down the river. We used to own a lot on it but we moved.