We have simulated the advance and retreat of Breidamerkurj¿kull, a tidewater glacier in Iceland, by means of a one-dimensional numerical ice flow model. The calculations were done with two different schemes for iceberg calving, the flotation model and the water depth model. The model simulates the glacier history by an advance into a lake filled by unlithified sediments without the occurrence of calving, followed by a retreat with calving into the excavated lake. The results indicate that the flotation model is not capable of producing the observed glacier retreat into deep water well, whereas the water depth model provides a glacier evolution similar to the observed retreat. The water depth model predicts that Breidamerkurj¿kull will retreat out of the lake after approximately 100 years under the present climatic conditions.