The pristine nature of river Ganges: its qualitative deterioration and suggestive restoration strategies

The river Ganges, the National Heritage, and the lifeline of millions of Indians, unfortunately, ranked the second most polluted rivers of the world in 2017. This review reveals the current trends of the water quality of the Ganges assessed around 36 stretches during 2012-2016, to indicate an improvement around 6 (16.7%), deterioration around 14 (38.9%), and non-significant changes around 16 (44.4%) stretches. An increase in dissolved oxygen and a decrease in biochemical oxygen demand were observed at six stretches (Devprayag [S₅], Rishikesh upstream [S₇], Varanasi upstream [S₁₉], Mokama upstream [S₂₅], Mokama downstream [S₂₆], and Munger [S₂₇]). The total and fecal coliform contamination decreased at seven stretches (Rudraprayag [S₂ and S₃], Devprayag [S₅ and S₆], Rishikesh [S₇], Varanasi upstream [S₁₉], and Munger [S₂₇]) due to improved hygienic conditions, but it increased subsequently at eight stretches (Haridwar [S₈], Kanpur [S₁₅], Raibareili [S₁₆], Prayagraj [S₁₇ and S₁₈], Patna [S₂₄], Berhampore [S₃₀], and Serampore [S₃₁]) due to improper defecation and mass bathing during 2007-2016. Dissolved oxygen level declined significantly, and biochemical oxygen demand increased (> 3 ppm), alarmingly at places receiving heavy untreated sewage water. The water quality of the Ganges was good up to Rishikesh, because of an undisrupted flow of the uncontaminated water from the higher altitudes (≥ 372 m) with higher forest cover, lower temperatures (< 21 °C), and higher dissolved oxygen (≥ 8.5 ppm) and due to the dissolution of antipathogenic chemical constituents of the medicinal herbs, pollutant degrading alkaline phosphatase, and bacteriophages. The present review is a systematic collection of data on river pollution, its scientific analyses, and its relationship with 6Ps (namely population, poverty, pollution, precipitation, plantation, and periodicity). Not only that, but the river water restoration measures have also suggested through the novel interlinked water working groups for implementing integrated water management strategies.