Plane like a speedboat
To switch the resultant Hydra Spyder into "marine mode," the driver simply presses a button, which drops the clutch, disengages the road drive and retracts the wheels.
The simple usage of a toggle button on the dashboard will enable the car's aquatic mode. The wheels then "tuck" into the body of the car, simultaneously switching to a different engine, ready to power the car on water.
Then the jet drive kicks in, allowing the Spyder to plane across water like a speedboat at more than 80km/h.
You can even have a built-in fishfinder, although this amphibian isn't intended for use on the open sea.