The first stage in the use of the San Juan River in the province of the same name, involves the Ullum hydroelectric plant with 45 MW of installed capacity, designed to supply the city of San Juan and neighboring districts as part of the Cuyo electricity grid.
The main structure, the movable diverter dam built at Punta Negra, 34 km from the capital of the province, has the function of impounding and diverting the waters of the San Juan river.