A patent was filed in June 1974 for the protection of the idea creating an amphibious bike. Benjamin Carter Locher of St. La Porte Texas created a bike which can be converted to use in water with an added propulsion and floating system . This was accomplished by attaching pontoons on both the front and rear of a bike.
A principal feature and object of the invention is to provide a readily retractable and deployable flotation gear that is adapted to be carried by the cycle in retracted position when the cycle is operated on the land and in the deployed position when operated in water.
Full patent information can be found here.