This lake is formed by the largest impact crater in western Europe, of a diameter of . The river leaves the lake at Leksand and continues south to its confluence with Västerdalälven. Västerdalälven is itself born of the confluence of two rivers, the Görälven and Fuluälven. These rivers have their sources not far from each other in Älvdalen Municipality in the Scandinavian Mountains. Fuluälven heads south along the east face of the mountain Fulufjället, while the Görälven flanks Fulufjället to the west, crossing the frontier with Norway where it takes the name Ljøra. After the confluence this river continues south, passing Sälen and then Malung and forking east to arrive in Vansbro Municipality. At Vansbro, it is met by the Vanån, its principal tributary. Its course then becomes more sinuous, tracing broad loops. It then enters Gagnef Municipality where it joins Österdalälven. From Djurås to the sea After the junction of the Österdalälven and Västerdalälven, the river heads east, passing Borlänge, Dalarna's largest city, then receiving the waters of the Lillälven, itself fed by the Faluån, a river which goes through Falun, Dalarna's second largest city. The river then continues to Avesta where it strongly changes character. It leaves a deep valley and enters into a flat country, uniquely marked by some eskers. During the remaining that it travels to the sea, the river, now called the Lower Dalälven (Nedre Dalälven), alternates between large bays () and rapids. This section is also characterized by regular flooding, sometimes over vast areas. The first rapids are those at Avesta, called Storfors and Lillfors (big chute and little chute), after which the river forms the lake Bäsingen, then the rapids Näs bruk, then the lake Bysjön. It forms the frontier between Västmanland County to the south and Dalarna County to the north. It then forms the rapids at Tyttbo, and right after, one of its largest fjärds, that of Färnebofjärden National Park, forming the frontier between Uppsala County to the south and Gävleborg County to the north. More than 200 islands are strewn over this fjärd. The river continues to the rapids at Gysinge and then another great fjärd, Hedesundafjärden-Bramsöfjärden. The river passes through the rapids at Söderfors towards Untrafjärden, then by the rapids of Untra towards Marmafjärden, and then the rapids of Lanforsen. Finally, goes through its last rapids at Älvkarleby before rejoining the Baltic Sea. History First humans and agriculture The