Someshwari River (also spelt Someswari), known as Simsang River in the Indian state of Meghalaya, is a major river in the Garo Hills of Meghalaya and Netrakona District of Bangladesh. It divides the Garo Hills into two parts.
Locally known as Simsang, the river starts from Nokrek Peak and runs towards east, passing through Rongrengiri, Williamnagar, the headquarters of East Garo Hills district, Nongalbibra, Siju, Rewak and finally Baghmara, the headquarters of South Garo Hills district. The chief tributaries are Chibok, Rongdik, Rompa and Ringdi rivers. The river has many scenic waterfalls in Meghalaya.
In Bangladesh it flows through the Susang-Durgapur and other areas of Netrakona District till it flows into the Kangsha River. A branch of the river flows towards Kalmakanda and meets the Balia River. Another branch of the river flows into the haor areas of Sunamganj District and flows into the Surma River. It is one of Bangladesh's trans-boundary rivers.