The word that describes maintaining your body on the water surface
Solution 1:
To flounder might be a suitable word.
From Google:
Flounder struggle or stagger clumsily in mud or water. "he was floundering about in the shallow offshore waters".
(To do it successfully would probably be treading water).
Solution 2:
You are looking for (to) float:
- to stay on the surface of a liquid and not sink:
- An empty bottle will float. You can float very easily in/on the Dead Sea because it's so salty.
(Cambridge Dictionary)