Scandanavia and Norway
Scandanavians believed in the Havfrue (merman) and the Havmand (mermaid), and a kind of merfolk called the neck. The neck were able to live in both salt- and fresh-water. The Norwegian mermaid was known as Havfine were believed to have very unpredictable tempers. Some were known to be kind, others to be incredibly cruel; it was considered unlucky to view one of these havfine.