Real Dictionary

tread water
to be in an unsatisfactory situation where you are not progressing, but are just continuing doing the same things
phrase: If someone who is in deep water treads water, they float in an upright position by moving their legs slightly.
phrase: If you say that someone is treading water, you mean that they are in an unsatisfactory situation where they are not progressing, but are just continuing doing the same things.

tread water in American English
to keep the head above water and the body upright without propelling oneself forward, by moving the legs and arms back and forth
to maintain the body erect in the water with the head above the surface usually by a pumping up-and-down movement of the legs and sometimes the arms

tread water in British English
to stay afloat in an upright position by moving the legs in a walking motion