Nallathanni is a major river originating from Anamudi Hills of Western Ghats , flows through Munnar town and later joins Muthirapuzha, a major tributary of Periyar River.

Being a reservoir of rich biodiversity ,Nallathanni virtually is a stream with crystal clear and quality water and hence known indigenously as "Nalla Thanni (good water)".

But by the urbanization of Munnar, owing to cater to the tourism demands, this river, which used to flow easily with quality water, turned into a waste carrier over time. It’s evident and unfortunate that sewage from many business establishments are directed towards the river. Moved by the plight of the Nallathanni and to redress this river pollution, a group of environmental enthusiasts joined hands on March 2, 2022 on the occasion of International Water Day, to organize a river cleaning campaign called “Veendum Nallathanni''in Munnar. Munnar Panchayat, UNDP, and other local NGOs including 32 voluntary groups and members from BRCS, VSSS, MEWS and RECITY had participated in the campaign. As an outcome of this campaign Nallathanni river has been restored and rejuvenated to its former stage,to its clean and beautiful stature . Efforts are being made to revive and sustain Nallathanni river in its past glory by the Haritha Kerala mission as a part of its ongoing waste management initiatives in Munnar