Abstract: An attachment for a bicycle is disclosed, permitting use of the bicycle in water, with relatively efficient propulsion and steering, and also on land, without removal of the attachment. Floats of the attachment are positioned on either side of the bicycle, connected by frame members which are removably attached to forward and rearward portions of the bicycle frame. The front wheel of the bicycle is provided with a solid circular disc, closing the space within the rim, so that the front wheel acts as a rudder in water when steered. Connected to the rear wheel spokes are a series of impeller cups or vanes which strike the water in the bottom of their stroke of movement to drive the bicycle forward. The floats may be of a lightweight foam material, or may be inflatable. For use as an exercising device, the bicycle may be provided with a resistance device engaged against the rear wheel, and the bicycle may be elevated on blocks, via the floats.