Agra (UP), Nov 29 : The Archaeological Survey of India (ASI) will undertake a year-long study to find ways to prevent the green-coloured stains on the Taj Mahal caused by the faecal matter of insects along the Yamuna adjacent to the monument. When the brown-green spots first appeared on the Taj Mahal's surface in 2015, caused by a tiny insect known as Goldie Chironomus, it was dismissed as a temporary issue by the authorities. An ASI official said that the spots were initially cleaned using a mudpack, but stains have been reappearing biannually, with an exception in 2020 when pollution levels in Agra were unusually low. An archaeologist at ASI, Rajkumar Patel, said that brown-green spots appear on the monument's north face adjoining River Yamuna. The ASI's chemical branch had devised a way to clean off these stains left by the faecal matter of the insects by washing it off with distilled water and then rubbing the surface with a clean cotton cloth, he said. However, since these stains are appearing year after year, it has become necessary to find a permanent solution to this problem. The ASI explained that the insects typically appeared in the Yamuna during March-April and September-October when temperatures ranged between 28-35 degrees. However, this year, the stains have lingered into late November, suggesting an unusual increase in insects and their extended breeding. Patel said that the ASI's Chemical Branch is undertaking an extensive study to understand the insect's breeding cycle, and proliferation conditions, and methods to prevent them from affecting the Taj Mahal. Meanwhile, the Agra Tourist Welfare Chamber has attributed the rise in pollution levels in the Yamuna to the stalled Taj Barrage construction project, which, if completed, could have controlled the situation. They have proposed either dredging the Yamuna to increase depth or constructing a barrage downstream from the Taj Mahal to ensure free-flowing water, preventing insect breeding that usually occurs in stagnant water. /IANS