One just says: She's floating.
As opposed to doing the crawl or doing the breaststroke.
In terms of swimming and associated skills.
Now, in terms of description, if you say She is floating in the pool., she is obviously not floating in the river or in the sea.
John: Where's Jean? Is she in the pool?
Mary: No, look, she's down there floating in the sea.
John: Yes, she loves to float, rather than actually swim.
Yesterday, we went down to the river. And there she was! Floating in the river.
- A swimming skill: floating
- Stuff (objects) that float: Balloons and floating mats (the latest craze!) and pool rafts float on water, for example.
- Scum and industrial waste floats on (the) water (horrible).
- And when someone finds a dead body in the water, one would describe that as: the body was found floating in the water.
- Lobster pots do not float in the water, they sink to the bottom of the ocean, for example.
In reference to people in swimming pools (or ocean or rivers or lakes) in terms of swimming:
Learn to float, floating, the skill, staying afloat, and by the way, she shows you how to float face down, too!:
- We love floating in the sea, never in pools. If you are specifying, the word is in for a person. But as I said, regarding pools, people generally just float. And we would not specify.