This is a great demonstration of a magnetohydrodynamic drive, which involves electric current being used as propulsion in water. When electric current is pass through a magnetic field its experiences a force which can be directed in such a way to be used as propulsion. In water or other liquids with lots of ions, this can be done by connecting a battery to two separated metal plates in the presence of a permanent magnet. The electric current from the battery causes the ions to move to the corresponding polarity and the magnetic field ejects them away, which thus forms the basis of a magnetohydrodynamic drive!
A schematic of the working principle is shown below.
