The eastern coast of the Jutland Peninsula, consisting of Danish Jutland and German Schleswig-Holstein features a type of narrow bay called Förde (plural: Förden) in German and fjord (plural fjorde) in Danish.
The words Förde, fjord and fjard are of the same origin as the English word firth, but today there are differences in the meaning between firth (Förde) and fjord in general.
When the area of the present Baltic Sea was covered by an ice sheet during the Weichselian glaciation, about 20,000 to 70,000 years ago, the edge of the ice moved on land as tongues of glaciers; these carved out channels.
The material removed formed moraine hills near the sides and ends of the channels.
Alternatively they have been interpreted as 'beheaded' river channels preserved beside a tideless sea.