A former coal mine in northwestern Spain has been transformed from a massive industrial pit into a large artificial lake offering an example of how degraded mining landscapes can be rehabilitated after extraction ends.
The As Pontes mine in Galicia was developed in the 1940s for the extraction of lignite, or brown coal. Over nearly six decades, around 260 million tonnes of lignite were extracted, leaving behind an open pit more than 300 metres deep.
The mine was closely linked to a large coal fired power plant operated by Endesa. However, stricter European Union air pollution regulations eventually led to the permanent closure of the mine in 2007.
Rather than leaving the enormous excavation abandoned authorities and engineers undertook a major environmental rehabilitation project. In 2008, the former mine pit began to be deliberately filled with water.
The process took more than four years and was completed on April 18, 2012. Around 547 billion litres of water were pumped into the enormous pit, creating what became one of Spain’s largest artificial lakes.
Creating the lake was not simply a matter of filling the mine. Engineers had to monitor how quickly the water level rose and how the changing conditions affected water chemistry.
Studies of the lake found that the water developed two distinct layers separated by a zone known as a chemocline. The upper layer is relatively oxygen rich and only mildly acidic, while the deeper layer has very little oxygen and significantly higher acidity. Researchers linked the separation to differences in the sources, temperature and mineral composition of the water.
Today, the former mining site has been transformed considerably. The lake covers around 865 hectares and includes a sandy beach, nature trails and areas used for recreational activities such as kayaking and canoeing.
Natural habitats have also developed around the shoreline, including meadows, scrubland, woodland and wetlands. Wildlife such as deer has returned to areas that were once dominated by mining waste and industrial activity.
The lake has also received Blue Flag certification recognising factors including water quality and environmental management. Tourism and recreation have become additional economic activities for the local area, which once depended heavily on coal mining for employment.
The transformation of As Pontes highlights the potential for carefully planned mine rehabilitation. Similar abandoned mining pits exist across Europe, Australia and the United States, although their environmental conditions vary widely. Some contain highly acidic or contaminated water and require extensive management.
As coal mining declines in many parts of the world, the As Pontes project demonstrates how former industrial sites can potentially be converted into new ecosystems and recreational spaces through long-term planning, scientific monitoring and environmental restoration.