A system of brackets and rails for attaching wheels, towing, and accessory devices to a pontoon water bike to increase the transportability and utility of the craft by making it towable by pedestrian and bicycle, converting it to amphibious operation, and allowing a variety of other attachments to create a more capable and efficient watercraft.

An improved human powered watercraft propulsion device and mounting frame for attachment to existing pontoon watercraft. The propulsion device is light weight, self-contained, portable, has few moving parts made from corrosive resistant materials, and is propeller driven for quiet, efficient, and environmentally friendly underwater propulsion. Having a simple twisted belt configuration with an open structural design, all of the components are easily viewed and maintained by the user, as well as continuously cleaned, cooled, and lubricated by the water during operation, without the need for a sealed waterproof housing and internal oil bath. Hand knobs provide belt tensioning during operation and the device is adapted for operation by pedal, friction wheel, or direct chain drive. The device is adjustable on the attachment frame to fit the operator, pivots when beaching or striking an underwater object, and components such as pulleys and the propeller are changeable to achieve different power ratios.