Places > East > Grímsá Grímsá Grímsá, a river formed by the two rivers Geitdalsá coming from lakes in the highlands east of Hornbrynja through Norðurdalur, and Múlaá coming from the Ódáðavötn lakes. Until it reaches the lake Skriðuvatn in Suðurdalur Múlaá is called Öxará.