Page "Baltic Sea" Paragraph 15

The ice extent depends on whether the winter is mild, moderate or severe.

Severe winters can lead to ice formation around southern Sweden and even in the Danish straits.

According to William Derham, during the severe winters of 1703 and 1708 the ice cover permeated as far as the Danish straits, parts of the Gulf of Bothnia and Gulf of Finland, in addition to coastal fringes in more southerly locations such as the Gulf of Riga.

This description would actually have meant that the whole of the Baltic Sea had been covered with ice.