If you think you can’t make yourself an Akwakat waterbike, then you are wrong. Li Wieguo, a Chinese from Hubei, China has made a human-powered amphibious bicycle similar to Akwakat and it’s relatively cheap and practical for you to Do-It-Yourself. Basic material/equipment you need is a classic bicycle and 8 sealed empty Gallons as the floating base, adjustable vane wheels as the driving power and some self-made frame for holding on the gallons so you can actually ride a bicycle across the lake.
Sadly, there is no valid blueprint for make one by yourself. You still need to going through the tries and errors to finally make one for yourself. But at least, you have the picture as the rough guideline.
(more info at InHabitat)