https://www.sciencedaily.com/releases/2018/07/180702111243.htm

This next generation HAMR uses multifunctional foot pads that rely on surface tension and surface tension induced buoyancy when HAMR needs to swim but can also apply a voltage to break the water surface when HAMR needs to sink. This process is called electrowetting, which is the reduction of the contact angle between a material and the water surface under an applied voltage. This change of contact angle makes it easier for objects to break the water surface.

Moving on the surface of water allows a microrobot to evade submerged obstacles and reduces drag. Using four pairs of asymmetric flaps and custom designed swimming gaits, HAMR robo-paddles on the water surface to swim. Exploiting the unsteady interaction between the robot's passive flaps and the surrounding water, the robot generates swimming gaits similar to that of a diving beetle. This allows the robot to effectively swim forward and turn.