I would like to add another ...

I would like to add another perspective. Water quality of the large surface bodies, like river Ganga is influenced by factors such as seasonality, location and flow. Low concentration of contamination will be observed at the time when the river carries large volume of water and opposite when smaller volume of water is present.

The national government is running a large programme for development and rejuvenation of the river. Institutes like IIT kanpur has done extensive research by gathering data from the multiple locations. Hence, lack of scientific data is not the reason.

Broadly, it is inadequate capacities of the urban local bodies to process the waste has led to current challenges.  Thus,  technical management and governance can improve the condition.