The Blue Lake is a nationally protected area located on the southern slope of Mine Hill, at an altitude of 530 meters. It covers an area of 0.5 hectares, has a depth of 4 meters, and an almost circular shape. This lake is unique due to its origins, as well as the chemical composition of the water and its distinctive color.

The Blue Lake was formed between 1919 and 1920, when water accumulated after the collapse of a mining gallery or surface works. It became known due to its beautiful color and the property of changing its shade depending on the season and weather conditions. The presence of iron sulfate in the water creates blue and turquoise reflections in spring (April-May), emerald green in summer, and a green-brown color in autumn. Surrounding the lake is a beautiful oak forest, as well as several pine trees that add a special charm to the area.

The Blue Lake was granted the status of a natural reserve of hydro-geological interest in 1977, and later in 2020.