Today's Image of the Day from NASA Earth Observatory features the Ruki River in the Democratic Republic of the Congo (DRC). It is a tributary of the Congo River, one of the largest rivers in the world by discharge and depth.  The Ruki River, previously known as the Busira, merges with the Momboyo River near the town of Basankusu to become the Lulonga River, which eventually flows into the Congo River at the town of Lisala. Dark waters of the Ruki River "If...