In the middle of the 20th century, with developments in hydroelectricity in Sweden, dams were frequently built across the northern rivers of Sweden. These barrages were also constructed in the national parks; the Stora Sjöfallet National Park lost nearly a third of its land area with the creation of a dam in 1919. In 1961, an accord called the "Sarek peace" ("Freden i Sarek") was forged, preventing hydroelectric developments in Sarek as well as in certain rivers, designated "national rivers". This also led to the establishing of Padjelanta National Park.