Lake Undozero Lake Undozero Lake Undozero () is a freshwater lake, located in the west of Plesetsky District of Arkhangelsk Oblast in Russia. It is one of the biggest lakes in Arkhangelsk Oblast and the second biggest one in Plesetsky District. The area of the lake is , and the area of its basin is . Lake Undozero is the source of the Undosha River, which belongs to the river basin the Onega River and thus to the White Sea basin. The lake has a sophisticated shape and contains a number of islands. The source of the Undosha is in the south-western
Onega River Monastery on an island in the Lake Kozheozero. Some of the finest monuments of the northern wooden architecture are located in the basin of the Onega, including ensembles of Lyadiny, Saunino Pogost, Krasnaya Lyaga, and Bolzhaya Shalga. These monuments also suffer from the lack of protection and their number steadily diminishes. In fact, the majority of them have been lost. The river splits into the Big Onega and Little Onega Rivers from its estuary, but then these branches join again, forming a big flat island. It freezes up in late October - early December and stays under the ice until