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Until five years ago very few people in Mumbai were aware of the Mithi river running through it. Then, in the monsoon of 2005 it flooded, drowning 500 people. With the devastation it erupted into public consciousness, dark and stinking. Ever since the authorities have been trying to revive it. Their latest experiment is putting it on oxygen. For three months oxygen was pumped into water along a kilometre stretch of the river to raise the level of dissolved oxygen.