Lac de l'Hongrin, reservoir in canton Vaud, Switzerland

Lac de l'Hongrin is a large reservoir in the canton of Vaud held back by a concrete dam. Several streams feed the lake, which supplies water to the regions below while being surrounded by green hills and meadows that create a calm landscape.

The two arch dams, Hongrin Nord and Hongrin Sud, were completed in 1969; all construction work ran from 1966 to 1971. The project caused tension for about fifteen years between the cantons of Vaud and Fribourg over the division of the waters. The dam holds 345,000 m3 of concrete, and its two arches are 123 m and 93 m high.

The lake lies in a military training area where the Swiss army conducts infantry exercises with mortars and manoeuvres with Piranha wheeled armoured vehicles, previously tanks and M-113s. Weekday access is often restricted or impossible. The dam is owned by Forces Motrices Hongrin-Léman SA of Lausanne.

The lake is accessible by car via a road leading to the dam where the route ends. The western side near La Lecherette offers easy walking paths on a quiet paved road that is suitable even for strollers.

The water level drops noticeably in autumn months, becoming especially visible in October. This natural fluctuation is part of the water management system and shows how nature and human planning work together.