The lake of Montbel or the Montbel dam is an artificial lake created in 1985 and located between the departments of Ariège and Aude.

With a surface area of 5.5 km2, it has a volume of water of 60 million m3.

It is located on the territory of the communes of Montbel and Léran, in the east of the department of Ariège and partly overflowing into the department of Aude.

This reservoir is located on the Trière, a small tributary stream of the Hers-Vif, it is fed by the waters of the Hers-Vif brought by a diversion located just downstream of the Peyrat at the departmental boundary of Ariège-Aude.

A maximum flow of 10 m3/s can be taken from the Hers, while the instream flow left to the river downstream of the intake is 1.2 m3/s.

The water stored in winter and spring, when the snow melts, is used to irrigate the Lauragais and Ariège plains and to support summer and fall flows on the Hers-Vif and beyond the Ariège and Garonne rivers.

The Montbel dam makes it possible to irrigate 28,000 agricultural hectares.

Reflection on the construction of the dam began in the 1970s, but it was in 1982, after a drought and long environmental impact studies, that work began and was completed in 1984.

This dam cost about 22 million francs and was financed by the Interdepartmental Institution for the Development of the Montbel Dam which groups together the three founding departments, Ariège, Aude and Haute Garonne.

Originally intended to serve agriculture, the dam has become over the years a major tourist attraction.

The banks and traffic have been developed with a picnic area, a campsite, a playground and a cultural space "La Maison du Lac".

The lake offers a multitude of activities such as canoeing, sailing, paddling, pedal boats, catering, horse riding, cycling, walking and of course fishing.

For fishermen, the lake is home to perch, catfish, pike, trout, pike-perch, pike-perch, roach.

Tourists and visitors will find their account and the same goes for the birds, many water birds wintering on the lake .

There are many ducks, coots and grebes.