Having a stroke often will decrease mobility in many patients. In fact, the CDC noted that if you have a stroke when you are over 65 years old, you have a greater than 50% chance of having reduced mobility as a result.
Fortunately, by rehabilitating in a pool, a stroke patient can have multiple benefits from the aquatic environment. First, the water provides buoyancy, helping to support the patient, especially if the legs are weak. With the buoyancy, the patient is more confidently able to work on balance, knowing that a wrong movement will be cushioned by the water. That surrounding water also acts as a source of natural resistance, allowing improvements and recovery in strength. The warmth of the pool water acts to help relax the muscles, and also reduce pain. Finally, the pressure of the water required greater effort, which can pay off in increased cardiovascular endurance.
These findings were supported by a study published in the Journal of Alternative and Complimentary Medicine, which found that water-based therapy following a stroke leads to improved lower extremity function and a marked improvement in qualify of life after a stroke. Well, that sounds like some very good news.
Sources: https://www.cdc.gov/stroke/facts.htm