The Drell River flows through the Eastern Lands and starts at the border between Galla and Scanra. It flows south and deposits into the Great Inland Sea, where it forms a delta that makes up most of Tyra. This delta is perhaps why Tyra is mostly swampland. It marks the eastern border of Tortall with Tusaine. Erosion from the river has created the Drell River Valley, of which Tortall owns one side and Tusaine the other. The river flows through the Tusaine Mountains, which also help make up the border.