These exercise pools are a resistance swimming apparatus, self-contained,
enabling the swimmer to swim in place. This is accomplished by accelerating
the water past the swimmer. Also known as a countercurrent swimming pool,
they usually consists of a water tank at least twice as long and about one
and a half times as wide as an average person with the limbs extended. The
swimmer swims unrestrained against an adjustable stream of water set in motion
by means of mechanical devices, such as jets, propellers or paddle wheels.