Hanoi needs millions of USD to revive riversVietNamNet Bridge - Hanoi is a ‘city of rivers and lakes’. The BOD5 (Biological Oxygen Demand) concentration in the rainy season is 1.09-2.08 times higher on Nhue River, and 1.1-2.18 times higher on Day River. The rivers are polluted by waste water from residential quarters and untreated waste water from production workshops. Hai said Hanoi has called for investments in waste water treatment projects from different sources, but the capital is just enough to treat 22 percent of waste water. In order to revive the rivers, Hanoi will need a huge amount of capital.