Water aerobics or "waterobics" is the performance of aerobic exercise in shallow water such as a swimming pool. In some areas it is known as AquaFit or "aqua aerobics", and is a type of resistance training.

Water aerobic workouts usually combine a variety of techniques from land aerobics, including walking or running backward and forward, jumping jacks, mimicking cross-country skiing, along with various arm movements. The workout also may incorporate equipment such as flotation belts, specialized water aerobics shoes, flotation devices, & ankle and wrist weights. The exercise can be done with music in water tempo, or without.

In addition to the standard benefits of any exercise, the use of water in water aerobics supports the body and reduces the risk of muscle or joint injury. The mitigation of gravity by flotation places less stress on the joints when stretching, and can allow a greater range of motion. The mitigation of gravity makes water aerobics safe for individuals able to keep their heads out of water, including the elderly. Exercise in water can also prevent overheating through continuous cooling of the body. Most classes last for 45-55 minutes.

Aqua aerobics requires access to a swimming pool via facilities, and in addition to any membership fees to access facilities, classes may cost extra. Although aquatic exercise greatly reduces the risk of injury, not as many calories are burned as would be in some other activities. Though aquatic activities in general expend more energy than many land-based activities performed at the same pace due to the increased resistance of water, the speed with which movements can be performed is greatly reduced.