It is located in the Pasvikdalen valley in Sør-Varanger Municipality in Finnmark county, Norway and in the Pechengsky District in Murmansk Oblast, Russia.

The nature reserve was established in 1992 (Russia) and 1993 (Norway), and it covers an area of 166.4 square kilometers (64.2 sq mi).

Located in the valley of Pasvikdalen, it protects the river of Pasvikelva and its vicinity, straddling the Norway–Russia border, with 31.4 square kilometers (12.1 sq mi) of its area being made up by water surface.

The segment in Russia, located within Peschengsky District, is 40 kilometers (25 mi) long and runs from Svanevatn in the north to Hestfoss.

The nature reserve covers the area of this stretch which is located within the Border Security Zone—i.e.

[5] The nature reserves center on the reservoir of Fjærvann, one of the few parts of Pasvikelva which remains intact largely as it did prior to the construction of the seven hydroelectric power stations along the river.

[8] The geology of the area formed at the transition of the Mesoarchean and Neoarchean Eon, 2.8 billion years ago.

[9] A belt known as the Petsamo Formation cuts through the reserve; its limestone-rich rocks give rise to birch, which contrasts the otherwise pine-dominated forests of the area.

The landscape consists of hills, moraines and melt-water deposits, supplemented with kettles and glacial erratics.

The landscape has been formed by two periods of ice sheets during the Quaternary glaciation, which has rounded all rock features in the area.

The 147-kilometer (91 mi) river has its headwater in Lake Inari and its mouth at Bøkfjorden of the Barents Sea, experiencing a total fall of 119 meters (390 ft).

[15] Most of the annual mean 358 millimeters (14.1 in) of precipitation falls during summer, qualifying the area as a semi-arid climate.

[18][19] Russian scientists have classified the vegetation as forest tundra and taiga, while Norwegian scientists have classified it as northern boreal ecosystem, with northern parts forming a gradient into an Alpine tundra zone.

[21] There are occasional areas with broad-leaved trees, including aspen, rowan, alder and goat willow.

[23] Mountainous species not commonly found in such wet and lowland areas include snow saxifrage and alpine chickweed and marsh Labrador tea.

The most dominant is rice mire, covered in marsh Labrador tea, cup lichen and heather.

The lower portion of the river previously had some Atlantic salmon, but these have all but disappeared since the hydroelectric stations were installed.

[26] Common birds include the black-throated loon, the bean goose and various species of ducks.

[36] The oldest archaeological finds in Pasvikdalen date to Stone Age and the Komsa culture.

[37] These nomadic people would arrive in the valley during summer and sustained themselves largely on fishing in the river.

[42] The area became part of the Finnish Civil War, when Finland secured a corridor to the Arctic Ocean.