Before the place became a town the name was Fosen (Fosna) and also Fossund. 'Fosen' meant 'hiding place', in this case probably '... from wind and waves', i.e. 'safe harbor'. However, there is a Norwegian word, 'foss(en)' that means (the) waterfall. Maybe it was King Christian VI in Copenhagen who misunderstood; his letter of permit also described the coat of arms for the new town. A modern version of this is shown below: A waterfall with three salmons on their way up. Well, this is a small island and there has never been a proper waterfall here. But when the map doesn't fit the landscape the obvious idea is to change the landscape. The depicted arrangement was made for the town's 250th anniversary. Unfortunately there hasn't been any rain lately so the waterfall is dry.
(2008-05-10)

Addendum: When visiting Kristiansund in 2010 two tiny ponds and a pump supplied the waterfall with water.