Many major Rivers of India and Bangladesh flow west to east before draining into the Bay of Bengal. The Ganga is the northernmost of these rivers. Its main channel enters and flows through Bangladesh, where it is known as the Padma River, before joining the Meghna River. However, the Brahmaputra River flows from east to west in Assam before turning south and entering Bangladesh where it is called the Jamuna River. This joins the Padma where upon the Padma joins the Meghna River that finally drains into Bay of Bengal. The Sundarbans is a mangrove forest in the southern part of the Ganges-Brahmaputra Delta which lies in the Indian state of West Bengal and in Bangladesh. The Brahmaputra at is the 28th longest River in the world. It originates in Tibet. The Hooghly River, another channel of the Ganga that flows through Kolkata drains into Bay of Bengal at Sagar in West Bengal, India.