The Koolibor River was located on the Napan Isles and was a source of fresh water for ships traveling Reacher's Ocean. During the island's dry season, Paralt snakes made their way down the river to the sea.
Before the conquest of Kartool, a younger Commander Nok went to meet the Kartool fleet in battle. He first brought his fleet of six dromons to the mouth of the Koolibor River to collect fresh water before making the voyage. Nok's sailors soon discovered that all of the barrels they filled in the Koolibor were infested with venomous paralt snakes, and the mission had to be abandoned.