Arkhangelsk Oblast the south-west of the Oblast drains into the Kema River which belongs to the basin of the Caspian Sea. The area in the Onega River basin containing the biggest lakes in the oblast, such as Lake Lacha, Lake Kenozero, Lake Undozero, and Lake Kozhozero. The tundra of the Nenets Autonomous Okrug also contains a number of bigger lakes. The river basin of the Pinega is characteristic of the karst, with a number of caves in the region. The White Sea coast within the Oblast is split into the Onega Bay (where the Onega is the major tributary), the Dvina Bay
Primorsky District, Arkhangelsk Oblast first-level administrative division of Russia kept changing. In 1930, the okrug was abolished, and the district was subordinated to the central administration of Northern Krai. In 1936, the krai was transformed into Northern Oblast. In 1937, Northern Oblast itself was split into Arkhangelsk Oblast and Vologda Oblast. Primorsky District remained in Arkhangelsk Oblast ever since. The location of the administrative center of the district was moved several times until Arkhangelsk finally became the center. On December 17, 1940, Belomorsky District was established on the Onega Peninsula, in the areas which previously were parts of Primorsky and Onezhsky Districts. The administrative