The National Highways Authority of India (NHAI) has informed the National Green Tribunal (NGT) that it was compelled to use a portion of a pond in Mamallapuram to construct an exit ramp for the East Coast Road (ECR) four-laning project between Mamallapuram and Puducherry. The clarification comes in response to a petition alleging that the construction encroached on the waterbody without valid justification.In its submission, NHAI project director M S Chaitanya said only 3,460 sqm — less than 20 per cent of the 15,000 sqm pond — was used, mainly along shallow edges. The area, he said, was necessary to create a safe exit for vehicles entering Mamallapuram from Puducherry, via a proposed underpass near the heritage elephant sculpture. Without the ramp, the accident-prone junction could become a major blackspot along the high-speed corridor, the agency warned.NHAI finalised the project alignment in 2018, awarded the contract in March 2020, and began work in May 2023. Objections were first raised in August 2024, with the NGT petition filed in January 2025.The agency cited an independent report from LN Malviya Infra Projects confirming that about 10,800 cubic metres of earthwork was undertaken in the pond area using non-polluting materials. It added that the embankment would not impact water quality, as the pond water remains largely static.To offset the impact on the Solaipoigai tank, NHAI said it carried out excavation at four other nearby lakes — Pooncherry, Perumaleri, Karanai, and Kuzhipandalam — creating over 45,000 cubic metres of additional water storage. The work, it said, supports the government's ‘Amrit Sarovar’ waterbody rejuvenation initiative.NHAI also said it had obtained a no-objection certificate from Tamil Nadu’s water resources department for the project alignment. Alternative routes, it added, were ruled out due to the proximity of a major bridge across Buckingham Canal, just a kilometre away, making any shift geometrically unfeasible and a threat to road safety.The NGT will hear the case again in June.