Experts at the Department of Environment have classified three rivers in the capital as "biologically dead."
Laboratory tests have proven that the water in most parts of the Buriganga, Turag and Balu rivers contains no dissolved oxygen and is therefore totally devoid of aquatic life.
A senior DoE scientific official said, "According to official standards, the minimum level of dissolved oxygen necessary to sustain life is 5 milligrams per litre.
"For the last several months we have found no oxygen whatsoever."
Whilst the Department of Environment (DoE) did not test toxicity, DoE experts said they believe the water in the three rivers is highly toxic and hazardous to the millions of people living along the riverbanks.
During the dry season the water flow in areas around the city is cut off by rising silt levels at the mouth of the Jamuna's main water conduit.
When the water source is cut off, millions of litres of industrial and household waste accumulates in the river.
Between early September and May the water turns deep purple and black and foul odours are common.
The only movement occurs when high tides push the water slightly upstream and the low tide downstream.
The situation is not likely to improve until the floodwater from the Jamuna River in Manikganj flows in during the rainy season.
The government is planning a Tk 1,000 crore mega-project to restore the flow of the rivers by dredging the source at Jamuna in Manikganj as well as diverting water towards Dhaka.
Indiscriminate encroachment and massive pollution have already prompted the government to declare these four rivers ecologically endangered.