40 non-exercising women were split into two groups with one group participating in regular aquanatal exercise and the other undertaking no regular exercise. The researchers report that immersion and the physical comfort created by buoyancy improved mobility and reduced post-exercise pain. The hydrostatic pressure and resulting increase in venous blood pressure and urinary elimination helped to reduce lower extremity edema and swelling and the associated discomfort. Overall, the participants in the aquanatal exercise program reported significantly less physical discomfort, improved mobility, improved body image, and more health-promoting behavious than the non-exercising group.
[S. Smith & Y. Michel: A Pilot Study on the Effects of Aquatic Exercises on Discomforts of Pregnancy in: Journal of Obstetrics, Gynaecology and Neonatal Nursing (2006) vol. 35, pp.315-323.]