Its construction had a considerable impact on the landscape. Indeed, its impoundment caused the immersion of part of the valley. Thus, bridges, houses or even the Firminy / St Just railway line found themselves engulfed in this reservoir.
Its function is primarily hydroelectric but the dam also allows river regulation and road crossing. The artificial reservoir it creates, Lake Grangent, allows the creation of recreational activities.

Majestic landscapes
The creation of the Grangent dam profoundly changed the landscape of the Loire gorges. The steep and dark gorges are succeeded by a luminous body of water allowing the development of tourist activities. The filling of the dam led to the immersion of infrastructures such as the Firminy-Saint-Just railway line, or even certain houses and bridges. Other hamlets, once sheltered from the floods of the river, are now found on the banks of the Loire, offering sumptuous landscapes, such as the peninsula of Châtelet, the Camaldules, or the island of the castle of Grangent. .
Modified ecosystems
With the creation of the dam, the Loire saw its flow decrease. Thus, whitewater fish such as trout and salmon, formerly enjoyed in the castles of Saint-Victor and Essalois, are giving way to species preferring calm waters (roach, carp, etc.). The water reservoir also encourages the arrival of other fauna and flora species of ecological interest. This diversity leads to the protection of the Loire gorges as a classified site, a Natura 2000 site and the placing of certain plots in the Regional Nature Reserve.
A “natural” territory dynamic
Today, this magnificent body of water offers us spectacular panoramas, as diverse as they are rich in great biodiversity, but also with a remarkable history. It allows the development of nautical and tourist activities in our region, with actors involved in the development of reasoned tourism and oriented towards "life-size" events!
Technical characteristics of the dam
The Grangent dam is of the "vault gravity" type. It is 200m long and 55m high.
Its reservoir maintained at its maximum level between June 1 and September 15 of each year offers tourists a body of water of 365 ha spread over 21 km, representing more than 57 million m3 of water.
It is equipped with 4 valves each measuring 14m high and 12m wide. They can evacuate up to 6000 m3 of water per second.
It produces on average the equivalent of the annual domestic consumption of a city of 50000 inhabitants.
You have been warned!
The production of electricity from hydroelectric plants leads to significant variations in flow, causing sudden rises in the water level of rivers. You have to move away from the river when the current speeds up and the water level rises. On a lake, near a dam, do not venture beyond the buoys. Obey signs and all signs near dams, canals and rivers.