Chança dam, Reservoir on the Spain-Portugal border in Huelva Province

Chança dam is a gravity dam on the international course of the Chanza, the last major left-bank tributary of the Guadiana, on the Spain-Portugal border in western Huelva province. Its crest is 338 m long at elevation 66, creating a 50 m drop, and it stores 341.38 hm³ for water supply and hydroelectric power. It lies just northeast of the Portuguese village of Pomarão.

Construction of the dam began in 1979 and was completed in 1985, the year exploitation started. It was built after the canal supplying Huelva's industrial zone, fed from the Guadiana at the Bocachanza pumping station, saw increasingly frequent seawater intrusion as large dams upstream of Badajoz altered the flow. The pumping station and dam were then jointly named Complejo del Chanza.

The name comes from the Chanza River on which it was built. For local residents and farmers, the water it holds shapes daily life and agricultural practices in the border region.

Access is easiest from El Granado in Spain or Pomarão in Portugal, connected by a bridge built in 2008. Water levels vary significantly with seasons, so riverbank areas and viewpoints may be more or less accessible depending on the time of year.

In severe droughts the reservoir has supplied the cities of Ceuta and Cádiz. The canal downstream, built before the dam for Huelva's industrial zone, once drew water directly from the Guadiana at the Bocachanza pumping station, feeding chemical plants and irrigated strawberry and citrus fields.