The project was planned in the early twentieth century to irrigate the La Loma area. Construction began around 1929–1930 and the dam was completed in 1944; the official opening took place in 1946. At the time, El Tranco was one of the largest reservoirs in Spain. The gravity dam is around 90 metres high and about 290 metres long along the crest. The hydroelectric power station is located at its foot.
The settlement of Bujaraiza disappeared beneath the water. In 1940 it was home to around three hundred people and had a church and a cemetery. Some of the families were relocated to a newly established settlement near Palma del Río. When the water level falls, remains of the former settlement can become visible on the reservoir bed. The castle of Bujaraiza stands on the island of Cabeza de la Viña and is particularly easy to see when the reservoir is full.
The settlement beside the dam once had a school, the San Rafael chapel, a small works store and a Guardia Civil post. Today it lies on the A-319, roughly halfway between Cazorla and Hornos de Segura. The settlement belongs to the municipality of Hornos, not Beas. In summer there are pedal boats and kayaks and, when the service is operating, a solar-powered boat also leaves from the jetty. Fishing is also common here. The reservoir is not a designated bathing area: signs at the dam prohibited swimming, the water is cold and the bottom is uneven.
- Tranco settlement and dam: View on map




