Via Hackster.io, researchers at the Imperial College of London have created an aquatic robot which can mimic a “flying fish” by launching out using a jet of water. Water from the environment is the propellant with a small amount of calcium carbide.
The fish-bot is controlled by an Adafruit Feather M0 board, along with a Bluetooth interface, pressure sensor, and inertial measurement unit. Impressively, it has only one moving part — a pump that pulls in water from the environment. Multiple launches can be accomplished after sucking in more water to use as a propellant.