Hydroelectric power plants generate electricity by harnessing the energy of water. The process begins with water stored at a height, which possesses gravitational potential energy. When this water is released, it flows downward, and its potential energy is converted into kinetic energy. This high-speed flowing water spins a turbine. The turbine is connected to a generator, which converts the mechanical energy of the spinning turbine into electrical energy.

The energy transformation is: $E_p\to E_k\to E_{\text{mechanical}}\to E_{\text{electrical}}$

Final answer: potential energy is converted into kinetic energy than to electric energy.