I recall a docco on the Ganges & the effort to clean it up. Around 20~ odd years back they launched a huge project to put waste treatment sites all up & down the river. They did, mostly, but then didn't follow up.
There was a brief time where the Ganges was "cleaner" but still bad. Then even by the time the docco was made it was rapidly getting worse again.

I was reminded of it because they spent a lot of time in Kanpur. The tanning industry is massive! And the waste is grotesque at best, deadly at worst. MOST of it goes straight into the river, no treatment at all. They tracked waste from one small tannery to prove this. The tannery people claimed they had no idea, they thought (they said) it went to the new waste treatment plant :/ The amount of waste that one small place produced was staggering. Rotten fat was the bulk of it, it apparently has a "unique odor" which is "unforgettable".

I remember Mike Rowe's "Dirty Jobs" episode where he visits a tannery in America. It probably was about the same size as the one in India, but produced a tiny fraction of the waste & that stuff was NOT pumped into the sewers but sent for treatment by truck, or to an incinerator. He said it was one of the worst jobs he'd experienced.