Agavanzal, Cernadilla and Valparaíso, the three Tera reservoirs contributing to renewable development in Zamora

Iberdrola España has a presence in three hydroelectric plants along the Tera River, a tributary of the Esla and one of the rivers in the basin with the highest rainfall. The Cernadilla, Nuestra Señora de Agavanzal and Valparaíso facilities are located in the middle stretch, below Lake Sanabria, in the province of Zamora in León. Together, they have a combined installed capacity of more than 120 MW and provide clean, renewable energy to thousands of Spanish families.

Presa Valparaíso

Hydroelectric plants in the Tera basin

Number of hydroelectric plants 3
Total installed capacity 124 MW
Number of households benefited 86.800
Year of first installation 1969

The Tera is located in the northwest of the Iberian Peninsula, being one of the most important tributaries of the Esla River. It flows through the province of Zamora, in Castile and León, from its source in the mountains of Peña Trevinca to its mouth on the Esla, draining a catchment area of 2,415 km² over 139 kilometres. It is the river of the basin of the same name with the highest rainfall: 1,800 l/m² annual average at its headwaters, in the Sanabria area.

Iberdrola España, in accordance with the priorities defined in the Water Law, takes advantage of this water resource offered by the Tera river basin through dams and hydroelectric power plants, which generate clean and pollution-free energyExternal link, opens in new window.  for thousands of families in this region of Castile and León. Furthermore, water management along the Tera is based on a clear principle of respect for local natural resources. The entire maintenance and operation process is carried out with the aim of minimising any impact on the environment, which means that our teams always seek to comply with all measures to protect the fauna and flora around our facilities.

Tera Reservoirs

The huge water storage reservoirs along the Tera River, known as “embalses” or “pantanos”, are mainly used for electricity generation through their hydroelectric power plants, but these water resources also have different functions of great benefit to the local population, such as irrigation, supply or recreational activities such as fishing and leisure. The three main reservoirs located in the Tera basin have a storage capacity of more than 453 hm³ of water and a flooded surface area of 2,982 hectares (ha), acting as key elements for drought mitigation in the province of Zamora.

Iberdrola España is active in three reservoirs in the Tera basin. These are: Cernadilla, Nuestra Señora del Agavanzal and Valparaíso

Cernadilla Reservoir

The Cernadilla Reservoir is located on the section of the river Tera that flows through the Sanabria region, in the northwest of the province of Zamora. The reservoir has a gravity-type dam of the same name with a flooded surface area of more than 1,394 hectares (ha). In fact, the Cernadilla reservoir is one of the largest in the region, with a total volume of 255 hm³ of water, a figure which makes it Iberdrola's third largest reservoir in Castilla y León, behind only those of Almendra (2586.36 hm³) and RicobayoExternal link, opens in new window.  (1148.08 hm³), also located in the province of Zamora.

Nuestra Señora del Agavanzal Reservoir

The Nuestra Señora del Agavanzal Reservoir is located in the Zamora town of Olleros de Tera, belonging to the municipality of Calzadilla de Tera. The Agavanzal project, named in honour of the virgin of the same name, was inaugurated in 1994 with the aim of irrigating the fields near the river and supplying water to nearby villages, as well as contributing to electricity production.

In some of its areas, the reservoir is fully suitable for use by the local population, who can fish during the relevant season or bathe in the permitted areas. Its reservoir has a total capacity of 36 hm³ of water and a surface area of 365 hectares (ha).

Valparaíso Reservoir

The Valparaíso reservoir covers an extensive area of 169 hm³ capacity between the municipalities of Mombuey and Villadeciervos, belonging to the region of La Carballeda. It has river beaches at the foot of the Sierra de la Culebra which are perfectly equipped for bathing, leisure and relaxation for the inhabitants of the nearby villages, including the Valparaíso beach.

The civil works infrastructure that makes it possible to dam the water of this reservoir is of the gravity type and built of concrete, this being the dam with the longest crest length of the entire Tera basin (540 metres).

(*) All the data provided on the capacity and surface area of reservoirs come from the specialised website Embalses.netExternal link, opens in new window. .

Hydroelectric Power Stations of the Tera River Basin

The significant volume of water stored in the reservoirs of the Tera basin makes this region a place of enormous water use. Our commitment to sustainability and the promotion of renewable energiesEnlace externo, se abre en ventana nueva.  is reflected in our commitment to hydroelectric generation in the Tera basin and the management of the three hydroelectric plants that we manage from the river's course through the town of Cernadilla to the municipal limits of Calzadilla de Tera.

The presence of the Cernadilla, Nuestra Señora del Agavanzal and Valparaíso power plants along the course of the Tera offers clear positive benefits and opportunities for the community in the region. In addition to providing a renewable source of electricity to the homes of thousands of families, the full operation of these hydro facilities maintains local jobs, promotes sustainable generation in the province of Zamora and boosts economic development.


In operation since 1969, being the oldest of the three facilities in the middle section of the Tera River, the Cernadilla outdoor-type hydroelectric power station is responsible for supplying energy to about 24,000 households in the area thanks to its total power output of 3,000 MW. to about 24,000 households in the area thanks to its total power of 34 MW. It has a gross head of more than 55 metres from the crest of the dam, making it the largest waterfall of the three plants that Iberdrola España operates along the Tera River.

Nuestra Señora del Avaganzal

The Nuestra Señora del Agavanzal dam, located in Calzadilla de Tera, has had an external hydroelectric power station of the same name in operation since 1995. Nuestra Señora del Agavanzal is the plant with the smallest installed capacity on the river Tera, with a total capacity of 24 MW, and the lowest head, at 35.5 metres, although it is the only facility that is divided into three generator groups. The renewable energy generated at the facility is capable of benefiting almost 17,000 households.


The Valparaíso hydroelectric power plant has two reversible vertical axis units with a total pumping capacity of 66 MW for a discharge head of 49 metres and a flow of 55.7 m3/s per group, acting as a "giant battery" that stores potential energy in the form of water in the upper reservoir. It is the plant with the largest electricity generation capacity in the Tera basin, directly benefiting approximately 46,000 households.

In May 2023, the Valparaíso plant achieved one of the major milestones in its history by activating the full operational pumping of its generator set 1, which resulted in an addition of 30 MW to the pumped storage capacity in Spain. Pumped hydroelectric technologies, which have been used in other projects developed by Iberdrola España, such as the Cortes-La Muela hydroelectric complex in Valencia, represent an efficient storage solution that favours the implementation and integration of renewable energies. 

‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎