Segozero, Freshwater lake in Republic of Karelia, Russia.

Segozero (Karelian Seesjärvi) is a lake-reservoir in the Medvezhyegorsk and Segezha districts of Karelia, in the White Sea basin. Its tectonic basin covers 815 km² at a normal headwater level of 120 m above sea level, with a catchment of 6,640 km² and more than 70 islands totalling 29.2 km². The shoreline is indented, and the elevated, rocky shores are almost entirely covered with coniferous forest. The Segezha flows out towards Vygozero; the Sanda, Pyulva, Voloma and Luzhma are among the rivers flowing in.

In 1957 a dam at the source of the Segezha River turned Segozero into a reservoir, raising the water level by 6.3 m. Its surface grew from 753 km² to 815 km² at normal headwater level. In the 1920s–1930s steamships such as Gustera and Imandra carried freight and passengers; on 19 October 1941 the Finns sank the Imandra by artillery fire during the evacuation of Padany.

The Karelian name Seesjärvi means "clear lake" (sees, "clear"; järvi, "lake"). The shores are the ethnic territory of the Segozero (Padan) Karelians, or lappi, a small sub-ethnic group of the Karelian people in whom anthropologists note Mongoloid traits brought by the local Saami substrate population.

The shores are mostly high, rocky and covered with coniferous forest, largely unpopulated and hard to reach; the lake freezes over in December and the ice breaks up in May. The water level varies by about 1.5 m on average, up to 2.49 m over the years. Access is by water or forest roads, so plan around the ice season.

Dülmek Island was declared a geological nature monument in 1984 for outcrops of pinkish-grey Upper Jatulian dolomites holding stromatolites and microphytolites, some found nowhere else. Between 1935 and 1938 marble was quarried at Dyulmyagi on the island, which gained production buildings, a pier and a boat service aboard the motor vessel Segozero.