In Norse mythology, the Vimur is the largest of the Elivagar rivers that were formed at the beginning of the world.
In Kevin Crossley-Holland's retelling of the Norse myths based on the writings of Snorri Sturluson, the Vimur river is mentioned in the tale of Thor and Geirrod. Thor needed to cross the Vimur on his way to Geirrod's abode. The river was at the time a mix of water and menstrual blood, the force of which threatened to sweep Thor away. The blood was issued by Geirrod's shamaness daughter, Gjalp, who stood astride the river. Thor stopped up the flow by hurling a rock into the source of the blood, effectively stopping the flow. This, with the help of a rowan tree, allows Thor to cross the river Vimur.