Puruvesi 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,...

 in Eastern Finland

Finland

Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

. The lake is located in Kerimäki

Kerimäki

Kerimäki is a municipality of Finland.It is located in the province of Eastern Finland and is part of the Southern Savonia region. The municipality has a population of and covers an area of of which is water. The population density is ....

, Kesälahti

Kesälahti

Kesälahti is a municipality of Finland.It is located in the province of Eastern Finland and is part of the North Karelia region. The municipality has a population of and covers an area of ofwhich is water. The population density is....

 and Punkaharju

Punkaharju

Punkaharju is a municipality of Finland.It is located in the province of Eastern Finland and is part of the Southern Savonia region. The municipality has a population of and covers an area of of which is water. The population density is...

 municipalities. Part of the Saimaa

Saimaa

Saimaa is a lake in southeastern Finland. At approximately , it is the largest lake in Finland, and the fourth largest in Europe. It was formed by glacial melting at the end of the Ice Age. Major towns on the lakeshore include Lappeenranta, Imatra, Savonlinna, Mikkeli, Varkaus, and Joensuu. The...

 lake system, it borders on the sub-lake system of Pihlajavesi to the south. As is the case of other lakes of Saimaa, it has numerous islands and consists of numerous many open lake areas, of which largest are Hummonselkä, Pajuselkä, Sammalselkä, Mustanselkä, and Ruosteselkä.

The lake is known for its pure water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and has uniquely good underwater

Underwater

Underwater is a term describing the realm below the surface of water where the water exists in a natural feature such as an ocean, sea, lake, pond, or river. Three quarters of the planet Earth is covered by water...

 visibility for a Finnish lake, easily extending to 6–10 meters from surface

Surface

In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...

 on calm and sunny days.

Recently, the Saimaa Ringed Seal

Saimaa Ringed Seal

The Saimaa ringed seal The Saimaa ringed seal The Saimaa ringed seal (Pusa hispida saimensis, is a subspecies of ringed seal (Pusa hispida). They are among the most endangered seals in the world, having a total population of only about 260 individuals. The only existing population of these seals is...

, a rare freshwater seal

Freshwater seal

The freshwater seals are the species of seals which live exclusively in freshwater bodies.The only true freshwater seal species is the Baikal Seal....

species, has returned to Puruvesi. Sightings of this animal have occurred frequently in 2006, 2007 and 2008. At least one seal was also sighted in the winter of 2009 as having wintered and given birth in the eastern part of Puruvesi.