Berg Lake is impounded by the Steller Glacier terminus. During the latter half of the 20th century and early 21st century this lake periodically drained west through a gorge to the Bering River. With retreat and thinning this outlet has been abandoned. Vegetation has regrown in portions of this channel area by 2024 illustrating this.
During the 1986-2022 period the full lake level declined, but the filled area of the lake remained close to 25 km2. The lake level decline led to abandonment of the gorge outlet and drainage south into Lake Ivanov (NWS, 2024). In 2019 this channel was also abandoned, and now the drainage goes directly from Pacman Lake into the Gandil River and then into the Bering River watershed (NWS, 2024). The rapid retreat of Steller Glacier terminus particularly on the western half of more than a kilometer from 2016 to 2018 has driven the continuation of outlet location shift. The speed of drainage from 2018-2021 caused significant flooding in the floodplain of the Bering and Gandil River, that has not been observed in 2022-2024.
The lake continues to fill each summer and drain in late summer, with drainage being in August of 2021 and 2022, and late July of 2023 and 2024 (NWS, 2024). It is evident that since the 2022 fill of 25 km2, that in 2023 and 2024 the lake did not completely fill before drainage, reducing flood hazards. The minimum lake size has declined as the water level has been reduced to 4 km2 by fall in 2022, 2023 and 2024. The lake depth is greatest in the glacier center, which drives greater calving and retreat. On May 19, 2025 filling is underway and the lake has an area of 6 km2.
