India and Bangladesh will redraw stretches of their border after several rivers that the two countries share have changed courses, washing away all signs of the divider, an Indian official said on Wednesday.

At many stretches, soil erosion has washed away border pillars, blurring the demarcation, or rivers have inundated the dry land border.

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"There is no border demarcation along about 175 km. The international boundary has to be redrawn in these stretches," said West Bengal's Malda District Magistrate Abhijit Chaudhuri.

"We are hoping to get on with this by next month and complete it before the next monsoon," Chaudhuri said.

Dhaka and New Delhi would form a joint team to carry out a survey to determine the international boundary before markers are installed.

India and Bangladesh share a 4094-km border.

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Indian officials say some 6,000 Bangladeshis, who come illegally in search of work, cross the border daily.

Bangladesh denies this allegation.

To stop this, India is building a concertina wire fence. Nature's forces aren't sparing these fencings either and Indian border officials often have to strengthen river banks to stop them from being washed away.

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Most bizarre are the charlands-- islands that appear in the middle of a river when it recedes after the monsoon-- so fertile they are quickly occupied by farmers from either side.

Sometimes they change every monsoon. Sometimes they acquire enough silt to survive for years. Often it is hard to tell which country the charland dwellers come from.