Experts at the Water Development Board (WDB) said the city is expanding so rapidly that in near future the townships and villages are likely to form part of it. The natural canals are vital not only for transporting people and merchandise to and from the capital but also for providing a 'fantastic drainage system' and reducing water logging in those areas.

"Remember Dhaka city once boasted 22 natural canals none of which is being saved and the consequences can be felt in the rainy season causing massive water-logging. Unless we act now to save them, we will face an environmental disaster," an expert said.

Some of the canals, serving mainly farmers, traders and commuters for decades, are fast being filled up by land-hungry city dwellers, who bought them and have proper documents.

About half the stretch of one such canal -- Atir Khal -- originating from the Buriganga at Waispur and rejoining it about 10 km downstream at Kholamora, has been sold off to individuals.

All over the canal, signboards have been hung to claim ownership. The canal was dredged in the late seventies under the orders of the then president Ziaur Rahman, local people said.

Most part of Atir Khal near Waispur is now dry due to a recently built road across it. A local brick kiln owner built the road by dumping earth in the canal. The manager of the brick kiln however said the road will be removed in the rainy season.

"Most part of Atir Khal was sold off to some influential people years ago. They bought it in connivance with officials at the deputy commissioner' office, Dhaka, and started demarcating plots and paying land taxes," said Shahadat Ali, a local schoolteacher.

The plots were later sold to hundreds of city dwellers.

Another canal -- Jinjira Khal, opposite Sadarghat launch terminal, is also in a sorry state. Although the canal still serves thousands of commuters and traders, residents and small industrial units along it dump solid waste gradually filling it up.

Alauddin Munshi, a trader who uses the canal for transporting vegetables and other merchandise, said if the authorities do not dredge the canal immediately it will cease to exist within a few years. "There are people in the area who are waiting to grab the canal," he added.

Ramchandrapur Khal, originating from the Turag river near Shoalmachi and joining Haikkar Khal about two km to the south and at Kalyanpur in the north in two streams, is also on the verge of extinction. Real estate owners have started filling up vast low-lying areas in the locality, also burying the canal bed.

Haikkar Khal in Mohammadpur, saved from being filled up thanks to a massive campaign by different environmental groups and The Daily Star is now in a poor state with knee-deep liquid tannery waste on its bed. The canal is also facing onslaught from budding real estate developers.

WDB officials said since independence, Dhaka has silently witnessed the extinction of at least 22 fast flowing canals criss-crossing it.

An engineer of the WDB said they had no plan to save the existing canals around the city.