Ogosta (Bulgarian: Язовир Огоста) is a lake and reservoir in the north-west of Bulgaria.

The second largest artificial lake in Bulgaria (after the Iskar Reservoir), and also in the wider Balkan Peninsula, it is one of the biggest in Europe.

Collecting the waters of the rivers Ogosta, Burzia, and Zlatitsa, the lake begins only 600 meters to the south-west of the edge of Montana city, and its surface is some 60 meters above the ground level of the city.

For the project two villages were flooded, Jivovtsi and Kalimanitsa, and their inhabitants were found new homes in nearby Berkovitsa and Montana.

Now the waters of the lake are used instead to generate electricity, and two hydro-electric power-stations called “Kosharnik” and “Ogosta” have been built below the dam.