A dam that has stood for over a century has now sparked an emergency in southern Spain, forcing the evacuation of 11,000 people from their homes as it comes just inches from its capacity, raising fears it could collapse. Montejaque Dam has stood for 102 years as a spectacular engineering failure, hidden amongst the mountains above Ronda in inland Andalusia.

As Storm Leonardo battered the province, the dam, which has long been dubbed the “Ghost Dam” by locals, was suddenly brought to life this weekend. The huge subterranean cave systems that have drained the Embalse de Montejaque reservoir for a century finally choked up, putting immense strain on the limestone gorge. As a result, Brits were among hundreds of people to be urgently evacuated from the Spanish holiday hotspot amid fears that it could burst its banks. 200 people were quickly rushed from the Estacion de Benaojan neighbourhood after terrified residents reported feeling the ground “tremble” from water gushing through limestone caves beneath their homes.

However, in an update on Monday, the number of people evacuated has soared to 11,000 people as the 36 cubic hectometre reservoir – equivalent to 14,400 Olympic-sized swimming pools – reaches its limit.

According to The Olive Press, a Ronda police source said: “They are worried about the dam, really worried. Whether it can hold or not. It’s now at a quarter of a metre from the top – it looks like it’s soon going to come over.”

“There is also the question about the 2,000 evacuated from Grazalema and the bedrock of nearby Benaojan collapsing,” they added. “The dam has never gotten that high and given its 100 years old everyone is very worried about it.”

“The question is, is there a way to let the water out safely before it breaks. It’s a nerve-wracking day here.”

Meanwhile, a source from GREA, the emergency centre coordinating the response, said there are “real fears” the dam might not hold.

Commissioned in 1924 by the Sevilla Electricity Company, Montejaque Dam took just nine months to build and now stands 272 feet (83 metres) high. Coming at a time when hydroelectric power was heralded as the future, Swiss architect Grüner was hired, who chose to utilise reinforced concrete rather than the traditional masonry blocks of the 19th century. This allowed for a curved design that directed water’s pressure into the canyon walls rather than relying solely on the sheer weight of the walls.

It was the first of its kind in Spain and, at the time, the highest dam in the country.

However, Grüner and his team failed to understand that the Sierra de Grazalema is a karstic region, not solid rock. The limestone mountains are like a sponge. Additionally, directly beneath the dam’s foundations was the Hundidero-Gato system – one of the largest and most complex cave networks in Europe. As such, no matter how much it rained, the water simply disappeared, escaping rapidly through the porous rock and emerging miles away at the Cueva del Gato (Cat’s Cave). By the 1940s, the project was abandoned.

Instead, for the past 80 years, the dam has served as a tourist hotspot for hikers and a nesting ground for the griffon vultures. However, the threat of Storm Leonardo has led to the dam’s notorious “plughole” being sealed over a century after its construction.