The Kumai River originates in the Schwaner Mountains and flows south for 179 kilometres (111 mi) to the Java Sea.[2] It empties into Kumai Bay.[3] The bay has a mud bottom that gives a good anchorage in a depth of 4 to 6 fathoms (24 to 36 ft; 7.3 to 11.0 m).[4] The river is navigable by vessels with a draft of 2 metres (6 ft 7 in) up to the village of Kumai on its right bank, 13 miles (21 km) from the entrance to the bay, and for 15 miles (24 km) further upstream.