Abstract: An underwater treadmill device is provided and includes a drive roller and an idler roller engaging opposite ends of a treadmill belt. A hydraulic motor is directly coupled to the drive roller for imparting rotary motion to the drive roller and the treadmill belt. The hydraulic motor is driven by a remotely located pump and electrical motor. The electrical motor drives the pump and thereby controls the speed of the hydraulic motor. The speed of the electrical motor may be controlled by a remote control unit which transmits signals in the electromagnetic spectrum. The idler roller does not include any bearings as a substantially frictionless portion rotates about another portion.