Širvėna Lake is a lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 located in Biržai municipality

Biržai district municipality

Biržai district municipality Lithuanian municipality, located in northern Lithuania, Aukštaitija ethnographic region, Panevėžys County.The towns of Biržai and Vabalninkas lie within the district. About 64% of its land is agricultural, including a number of organic farms...

, northern Lithuania

Lithuania

Lithuania , officially the Republic of Lithuania is a country in Northern Europe, the biggest of the three Baltic states. It is situated along the southeastern shore of the Baltic Sea, whereby to the west lie Sweden and Denmark...

. It is the oldest artificial lake

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

 in Lithuania. It was created in 1575 when the dam

Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

 was built on rivers Agluona and Apaščia

Apaščia

Apaščia is a river of Biržai district municipality, Panevėžys County, northern Lithuania. It flows for 88 kilometres and has a basin area of 893 km².It is a tributary of the Nemunėlis.-References:...

. The lake was built to protect the Radvila castle in Biržai

Biržai Castle

Biržai Castle is a castle in Biržai, Lithuania. Construction of the earth bastion-type castle started in 1586 by the order of Krzysztof Mikołaj "the Lightning" Radziwiłł. In 1575, preparing for this construction, a dam was built on the Agluona and Apaščia rivers at their confluence, and the...

. Now the city of Biržai

Biržai

Biržai is a city in northern Lithuania. Biržai is famous for its reconstructed Biržai Castle manor, and the whole region is renowned for its many traditional-recipe beer breweries.-Names:...

, which was built around the castle, is located on the southern shore of Širvėna lake. The suburb of Astravas is built on the northern and the suburb of Rinkuškiai on the western shore.