How has Dhaka become unlivable?

Dhaka's air is one of the most toxics in the world; pitch-black polluted water runs through its rivers, canals; tap water contains hazardous chemicals and cholera pathogens; the traffic here are unbearable, the roads are death traps -- Dhaka has now become an unlivable city stuffed with over 2.2 crore people.

Why is this four hundred year old city crumbling down now? Why nothing effective has been done to save the capital?

In Straight from Star Newsroom, Zyma Islam tries to find the answers with The Daily Star Deputy Chief Reporter Mohammad Al-Masum Molla.