water aerobics
The performance of aerobic exercise in fairly shallow water such as in a swimming pool. Done mostly vertically and without swimming typically in waist deep or deeper water, it is a type of resistance training.
en-US/ˈwɔtɚ ɚˈoʊbɪks/
en-GB/ˈwɔːtə ɛəˈɹəʊbɪks/