Water based resistance training and aqua aerobics are a load of bollocks!
Exercise programs such as water/aqua aerobics can actually provide a great way for people of all fitness levels and abilities to engage in some physical activity.
The buoyancy of the water means that there is a lot less impact on muscles and joints if pain and injury are a concern, but it can also help to provide a fantastic full body workout that combines both resistance training as well as cardiovascular training.
Difficulty can also be altered by changing the depth of the water that you are exercising in. The deeper the water the harder the workout.
This is also a great form of exercise for rehab or people recovering from illness or specific conditions like spinal trauma.