Nøkk (Nøkks proral) are Norse water spirits.

Magnus Chase and the Gods of Asgard

The Hammer of Thor

While Alderman was in possession of a cursed ring, he came under the deluded impression that all the guests at one of his parties were trying to steal his fortune. To prevent this he summoned the water spirits to destroy his guests. They were stopped with the combined efforts of Hearth and Jack.