CBP has a riverine force, which is a group of specially trained Border Patrol Agents that uses a fleet of water craft to patrol along the Northern and Southwestern borders. The ríverine force works closely with CBP's Air and Marine Operations (AMO). If a body of water on the border is so large that the far shore is not visible, then that body of water is patrolled by AMO instead of the U.S. Border Patrol.