The paper presents the general scheme and the relevant implementation of a Maximum Efficiency Point Tracking (MEPT) system for a Small Hydro Power (SHP) plant equipped with a variable-speed generator. This last consists of a Doubly Fed Induction Generator (DFIG) and a power electronic converter that independently controls both the rotor speed and the generator power factor. The MEPT is designed to be used with a propeller turbine with adjustable runner blade angle and it is coupled with the headwater level regulator. Such a regulator imposes the water flow to the turbine. The conceived MEPT periodically tries to improve the production efficiency by solving a constrained optimization problem, subject to the feasibility operating constraint of the SHP unit and to the equality constraint which forces to meet the water flow value provided by the headwater regulator.