It is a tributary of the Surma river, which originates from the Umngot River in Meghalaya.

The river enters Bangladesh through Sylhet district.

Where once large plied the Piyain, floods of the 1980s, unplanned quarrying of stones and illegal sand extraction have combined to leave the river largely dry.

[1][2] The length of the river is 145 km.

[3] Originating from the Umngot, the river enters Bangladesh through the Jaflong area of Gowainghat, getting divided into two parts.