An isthmus of shifting sand has separated the Limfjord from the North Sea during historic times. The present inlet, Thyborøn Channel, has existed only since 1862. A passage also existed during the Viking Age. Based on place names and the geography it is thought to have been to the south of the present one, between Ferring Sø (locally still called 'the Fjord') and Hygum Nor. Canute the Great sailed into it in 1027 on his way back from England. According to Saxo Grammaticus it closed at some time around 1200. There are records of several floods piercing the isthmus during the 16th to early 19th century.