Giving DDA and UP government three weeks' time in which to make their submissions, NGT also questioned the exceptions made by them in allowing some structures to come up at river fronts.
"We direct... The state of UP and DDA to file a report showing what their policy is on the floodplain area," said a bench headed by NGT chairperson Justice Swatanter Kumar.
The bench also directed DDA and UP government to apprise it about "whether they have declared floodplain areas under their respective jurisdictions and, if so, the nomenclature given, like 'Zone O', and other details.
"Let the power of carving out exceptions also be placed before us," it said.
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NGT also questioned Delhi government and DDA for allowing certain structures like Commonwealth Games village and Akshardham temple to come up at the river front and inquired as to what the policy was for making such exceptions.
"What is so unique about the CWG village that it can come up (on the floodplains) but others can't. So, it will be your discretion which building will come up and which will not.
"Please give us a complete affidavit and please be careful," the bench said.
NGT made note of submissions by the Advocate General of UP that the state government had already passed 32 orders whereby it was held that construction at river fronts was unauthorised and directed that the said orders be placed before it.
NGT is hearing a plea by UP-based water conservationist Akash Vashishtha who has alleged that farmhouses, colonies and commercial structures on the river bed caused damage to the environment and were in violation of the Environment Protection Act, 1986.