The Ancylus Lake existed approximately from 9500 to 8000 years B.P. calibrated, during the full Boreal period. The lake became the Littorina Sea when rising sea levels broke through the Dana River forming the Great Belt. This transformation was gradual as salt-water had begun to enter the Ancylus Lake 8800 years B.P. The salt-water that entered the lake diluted constituting episodic brackish water pulses. The proper end of the Ancylus Lake came however 7800–7200 year B.P. when Øresund was flooded causing a massive inflow of salt-water.