Eutrophication, or hypertrophication is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of plants and algae. This process may result in oxygen depletion of the water body

•  Thehuge quantities of organic load in the form of sewage from nearby townships are regularly reaching the river system. This is contributing to the eutrophication resulting in the change of colour.
• River Periyar flows in the state of Kerala. It originates in the Western Ghats and flows north for a short distance to Periyar Lake. Periyar Lake. is an artificial reservoir created by Mullaperiyar Dam across the river.
• Further downstream Idukki dam is constructed across the river. The river descending out of the mountains into the coastal plain and empties into the Arabian Sea.