Acid mine drainage (AMD) is formed when water and air come in contact with pyrite (FeS2) present in coal and exposed rocks, to form sulphuric acid. The process of pyrite oxidation further leads to the formation of Fe3+ and some or all of this Fe3+ precipitates to cause red, orange or yellowish colour of the water. The coal deposits in Meghalaya, India along the southern fringe of Shillong plateau are distributed in Khasi, Garo and Jaintia hills . Among these, the East Garo Hill region is a major producer of coal, and coal excavation is commonly done by primitive mining method known as ‘rat-hole’ mining . In the present study, it has been observed that more than 100 km stretches of the Simsang River are severely affected due to coal mining.