The water spirit in Frozen II is Nokk. In the film, Nokk appears as a powerful water horse guarding the dark sea route to Ahtohallan, the mythical river connected with the past.
Elsa encounters the spirit while trying to cross the dangerous ocean. Nokk initially resists her, but Elsa eventually uses her ice powers and determination to tame it. She then rides Nokk across the waves toward Ahtohallan, making the spirit an important part of her journey rather than merely a background creature.
The name comes from the nøkk, a water spirit in Scandinavian folklore. Traditional stories portray the nøkk as a supernatural being associated with lakes, rivers, or waterfalls, sometimes taking the form of a horse. Frozen II adapts that folklore into a majestic elemental guardian. It is often confused with Gale, the wind spirit, or Bruni, the small fire spirit.