Life originated in water and later major civilizations on earth also thrived on the banks of some of the largest flowing water bodies in the world. All living organisms are inherently dependent upon water for their survival. Water has fundamentally crucial role in ecosystem, biogeochemical cycling and biosphere as a whole (Das and Panda, 2010) and makes life as we know it possible on earth. Nearly 70% of blue planet’s surface is covered with water but almost 97.5% of it is saline water, only 2.5% of total is fresh water (Stiassny et al., 1999). Out of that 3% freshwater, only a little more than 1.2% sustains life (U.S Geological Survey, 2016). Majority of this surface water percentage is found locked up as ice, permafrost, glaciers and rest is found distributed in various lotic and lentic water bodies. Rivers, one of the most important lotic water systems on earth constitute only 0.49% of total surface freshwater (U.S.G.S, 2016), but this small fraction supports a plethora of life and this is where humans get a large portion of their water from. Of all the available surface water, freshwater biota is confined to only 0.01%, yet these ecosystems are highly diversified (Leveque et al 2008). Not just aquatic species, all terrestrial life depends on these high functioning ecosystems. They play a vital role in the life of human beings providing critical provisioning and regulatory services, basis of economic activities and wide range of cultural services (WWF Guide D, 2011). According to World wide fund for wildlife (WWF, 2006), intact freshwater ecosystems provide largest services to welfare of mankind. Ranging from supporting functions such as providing habitat, maintenance of biodiversity, primary production, nutrient cycling (Gomez-Baggethun & De Groot, 2010) to provisioning functions such as drinking and irrigation water supply, economic services such as industrial and manufacturing processes, hydroelectric generation and also being the centres of cultural, recreational, aesthetic, spiritual and religious heritage, (Vorosmarty et al., 2005) rivers are indispensable to mankind.
Unfortunately, riverine systems all over the world are under the strong developmental pressure due to unprecedented increase in population. With increase in population the demand for clean water for drinking, along with irrigation and hydroelectric generation has also increased (Engel et al., 2011; UN Millenium Project, 2002). Population expansion, industrialization, urbanization and constant efforts of mankind for improving living standards often come with a cost i.e pollution (Pearson, 1965). Overuse and degradation of freshwater quality by humans have now reached to a point where shortage of safe water is likely to limit food production, ecosystem function, and urban water supply (Jury and Vaux, 2007).