Uttar Pradesh's chief conservator of forests (wildlife) Sushil Awasthi began the survey in Kanpur.
It will be conducted downstream of the Ganga from Kanpur till Farakka Barrage in West Bengal, covering 1,100 km, sources in the Union water resources ministry said.
The Dehradun-based Wildlife Institute of India (WII), is enumerating aquatic life in the Ganga for the government under the project titled 'Biodiversity Conservation and Ganga Rejuvenation', with an aim to "re-construct" the river's biodiversity profile.
Led by WII senior scientists SA Hussain and Ruchi Badola, the phase two of the survey will be carried out by a seven- member team.
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The phase one of the survey, carried out the upstream of the Ganga between Bijnor and Kanpur from April 14 to April 25 had thrown up a few encouraging nuggets, suggesting the biodiversity in that 570 km-long stretch is "very active".
For the first time in 70 years, presence of Siebold's smooth scaled water snake in the river was reported by the WII.
During the survey, several new nesting sites of Indian Skimmer, a declining species which preys on aquatic animals from the river surface, including one in Allahabad was spotted.
Usually, the Indian Skimmer is found in the National Chambal Gharial Wildlife Sanctuary, located at the tripoint of Rajasthan, Madhya Pradesh and Uttar Pradesh and in the Mahanadi river basin.