The average DO level in the Buriganga dropped to 3.78 milligram (mg) in a litre of water in 2002-03 from 4.43 mg in 2002-02, according to the Department of Environment (DoE).

"Pollution of the river runs low from November to April. At some points such as the main discharge drain of tannery waste, at Chadnighat and Dholaikhal, the DO level slips to zero," said Omar Faruque Khan, director general of the DoE.

"Water becomes so polluted that even bacteria won't survive."

"In winter, the DO level ranges between 0 and 0.3 mg in a litre, far below the standards of 5 mg."

"In monsoon, the level of pollution is less as natural cleanliness and dilution keep the river flow normal," Khan said.

Apart from Hazaribagh and Dholaikhal, the average DO level is above 5 mg in a litre.

"The key pollutant choking the Buriganga is sewage. At least 70 percent sewage of the city stream into the river," Khan said.

"The tanneries at Hazaribagh are another major drag on the river. If they are shifted to some other places, the river may get some respite," Khan added.

The government has recently decided to shift 400 tanneries from Hazaribagh to Savar in the next three and a half years.

A central treatment plant will treat the tannery waste to prevent pollution.

"Industrial waste of the city is also channelled into the river. The waste, laden with heavy metals like lead and chromium, also contaminates the river," said Khan.

An inter-ministerial committee is working to make the river clean and demolish illegal structures on it.

"We will have to raise the navigability of the river. The flow of the river will gather pace if it is free from pollutants," Khan said.