India, Aug. 21 -- On Tuesday, the Mithi River did what Mumbai had long feared - it pushed back.

After five days of relentless rain, the river surged to 3.9 metres, breaching the Central Railway's 2.7-metre danger mark, submerging tracks and paralysing train services for over eight hours. The timing couldn't have been worse: a 9:16am high tide blocked the floodwaters from draining into the Arabian Sea, forcing the river to back up onto the streets. The overflow flooded parts of Kurla, BKC and Santacruz, with LBS Road, Taximen's Colony and Kapadia Nagar among the worst hit.

For decades, the Mithi has been treated less like a river and more like a dumping ground. Today, it is choked with untreated sewage, industrial effluents, plastic wast...