The Barun River (Nepali: बरुण नदी) is a tributary of the Arun River and is part of the Kosi River system in Nepal. The Kosi or Sapt Kosi drains eastern Nepal. It is known as Sapt Koshi because of the seven rivers which join together in east-central Nepal to form this river. The main rivers forming the Kosi system are – the Sun Kosi River, the Indravati River, the Bhola Kosi, the Dudh Kosi, the Arun River, Barun River, and Tamur River. The combined river flows through the Chatra gorge in a southerly direction to emerge from the hills.