Akkeshi-ko (厚岸湖) is a brackish lake near Akkeshi in Hokkaidō, Japan.

The wetlands of Lake Akkeshi and Bekanbeushi Marsh (別寒辺牛湿原) have been designated a Ramsar site.

Lake Akkeshi, 11 metres (36 ft) deep at its deepest point, is fed by the Bekanbeushi River (別寒辺牛川) and adjoins Akkeshi Bay.

[2][3] Since a part of this lake does not freeze, whooper swans and ducks winter there.

[5] Fishing and the aquaculture of oysters and clams occur in the lake.