Abstract: An amphibious vehicle has a drive system comprising a driven wheel (16) of the vehicle with which is associated a guide (38) having inlet (44) and outlet (46) means and the wheel being formed such that when the wheel is in water its rotation draws water into the guide via said inlet, compresses that water and feeds it to the outlet. The driven wheel of the vehicle has the form of an impeller operable to draw water into the guide and feed it to the outlet means. The guide is formed in two parts on opposed sides of the wheel, the first part having one or more apertures opening forwardly of the direction of movement of the vehicle and forming inlet means whilst the second part has a jet rearwardly and upwardly of the direction of forward movement of the vehicle. Each part is formed with means providing a seal between it and the rim of the driven wheel. The parts are carried with the driven wheel. The vehicle described is motor tricycle having a pair of front wheels and a single rear driven wheel.