The Pacific lamprey has inhabited the rivers, streams and coastal waters of the west for 350 million years (BPA, 2005). These data describe areas of suitable habitat currently and historically used by Pacific lamprey populations. Pacific lamprey, Lampetra tridentata, (more recently identified as Entosphenus tridentatus), are native to the Pacific coast from Baja California to the Bering Sea. They are anadromous, migrating from their natal stream to the ocean and back, but unlike salmon, Pacific lamprey spend well over half of their total life cycle in freshwater. Distribution data is mapped at a 1:24,000 scale statewide and are based on the StreamNet Hydrography dataset.