This is my 3D printed version of cardboard fish from little experiments for kids book. When you use cardboard material for fish you have just few minutes before it will soak up water and will sink. So i decided make one from PLA on Prusa i3 MK3 3D printer:)
I have added Fusion360 file so you can edit or even improve it if you wish;)
Just place it carefully on top of water surface and when it is floating drop some dishwashing detergent in the big hole in the middle of the fish.
Then after few seconds fish will start moving and increasing its speed!
You can use it as simple experiments for kids or just for fun:)
Prusa i3 MK3