The Goesvatnet is a lake whose water is dammed by the Gås Glacier. It undergoes periodic subglacial and inglacial drainage, usually in winter. When fully filled it is about 60 m deep and has the surface of about 1 km2. An attempt was made to explain the mechanism of the drainage of the lake. Changes in the situation and range of the lake over the period of 81 years were investigated. The magnitude and character of the deglaciation of the front part of the Gås Glacier were determined. A strict relationship was found between the drainage of the lake and the presence of naled ice in the extramarginal outwash (Gåshamnoyra).