"No one disputes that the island city on the Arabian Sea had more than its share of rainfall recently - some parts of the suburbs are reported to have received 94cm (37 inches) of rain in a single day last week.
Mumbai's storm water drains are designed to shut during high tide. This prevents tidal water from entering the city, but on very rainy days, it also prevents rainwater from draining out.
"But the water that collected in the city should have ebbed when the tide receded," says Bittu Sahgal, one of India's best-known writers on environmental issues.
"Why didn't that happen?"
Mr Sahgal blames the Bandra-Worli Sea Link, an ambitious flyover project that has come under fire from environmentalists for making ecological compromises.
The flyover crossing the sea, he says, has pinched the mouth of the Mithi River that drains most of Mumbai's excess water out into the Arabian Sea.
That's not all.
The systematic destruction of about 1,000 acres of the city's mangrove cover - what's left, about 5,000 acres, is under threat - has deprived Mumbai of its natural flood-barrier and silt trap.
Now rainwater washes silt into the bay, threatening to clog the city's deep natural harbour.
"Ecologically unsound decisions have caused huge financial damage," says Mr Sahgal."
Horror stories abound of urban welfare projects gone terribly awry. A World Bank-funded urban transport project has cut away hillsides, dumping debris on the city's wetlands.
Mangroves have been cleared to build golf courses, amusement parks and rubbish dumps. Building construction is planned even on 5,400 acres of salt pan land.
"In the post-tsunami scenario, this is plain lunacy," says Debi Goenka, executive trustee of Conservation Action Trust, an environmental NGO."