Nickar are demons or spirits. In Scandinavian, Teutonic, Finnish and Saxon mythology, Nickar are malevolent water spirits who drown people, torment fisherman, tip over boats and throw them to the tops of shore-side trees. According to mythology, Nickars or Hnickars patrol the waters of Scandinavian fjords, where they cause tempests, hurricanes, hailstorms and blizzards.
They have fish-like tails and often sit by the water combing each other's long green or blonde hair with seaweed, playing a harp or singing. Like the Sirens, they drag to the bottom of the sea anyone who ventures too close.
Nickar are descendended from the Mermen and Mermaids, or from the Nymphs of the Elbe and the Gaal, the Nixies (Teutonic) which are kind, loving benevolent water spirits, known to rescue wayward fishermen. These lesser water divinities will sometimes leave the water to attend nearby celebrations and dance or fire festivals, where they dance and greet local fishermen.
It has been suggested that "Old Nick", one of the colloquial English names for the devil, is derived from Nickar, but it seems more likely to be a contraction of the personal name "Nicholas" instead.