Even as he awaits a response from Karnataka Chief Minister D K Shivakumar for a proposed meeting on the immediate release of Cauvery water, Tamil Nadu Chief Minister C Joseph Vijay has drawn a firm constitutional line on another, much larger question: the proposed Mekedatu dam.In a detailed letter to Prime Minister Narendra Modi on Monday, Vijay urged the Union government to withdraw a recent parliamentary reply by the Ministry of Jal Shakti, arguing that it overlooks settled legal principles governing interstate rivers and the rights of downstream States.The intervention is significant because it separates two disputes that often become politically intertwined. One concerns Tamil Nadu’s immediate demand for water during a distress monsoon year. The other concerns Karnataka’s long-term proposal to construct the Mekedatu balancing reservoir. While the Chief Minister has sought political dialogue with Karnataka on the first issue, his letter to the Prime Minister makes clear that the second must remain firmly anchored in the legal architecture created by the Cauvery Water Disputes Tribunal and the Supreme Court.Vijay wrote that he wished to draw the Prime Minister’s attention to the Union government’s reply in the Rajya Sabha stating that the Supreme Court’s judgment of February 16, 2018, “does not expressly stipulate that Karnataka should obtain the consent of the lower riparian States before constructing a structure across the River Cauvery.”Calling that response “disappointing”, Vijay said it appeared to have been issued “without taking into consideration the prevailing legal position and settled law with regard to the consent of the lower riparian states.”To support his argument, Vijay cited the Constitution Bench judgment in State of Karnataka vs State of Andhra Pradesh relating to the Alamatti dam dispute.Quoting paragraph 100 of the judgment, he reminded the Prime Minister that the Supreme Court had held: “Nor can Karnataka State be permitted to construct up to that height without the consent of all other riparian States as well as without the approval of the Central Government.”Story continues below this adThe CM argued that the Cauvery Water Disputes Tribunal’s final award, later affirmed with modifications by the Supreme Court in 2018, similarly limits the powers of basin States. He pointed out that Clause XVIII of the Tribunal Award permits each State to regulate waters within its territory only “in a manner not inconsistent with the order of the Tribunal.”According to Vijay, any new project capable of affecting the regulated flow of the river must therefore first be examined for consistency with the Tribunal Award itself. The letter goes beyond citing legal provisions and attempts to demonstrate how the Tribunal has interpreted such principles in practice.Draws parallel with Kerala projectVijay referred to Kerala’s Pambar hydro-electric project, where the Tribunal required Kerala and Tamil Nadu to jointly agree upon release schedules despite the project involving only 0.1 thousand million cubic feet of consumptive use.“This demonstrates that the Tribunal attached paramount importance not merely to annual quantities but also to coordinated regulation of releases affecting lower riparian interests,” he wrote.Story continues below this adHe further referred to Clause XI of the Award, which, according to the letter, prohibits any upper riparian State from taking actions affecting scheduled deliveries to downstream States except through mutual agreement and consultation with the regulatory authority. Clause XX, he noted, recognises that modifications to the Award can be achieved only through agreement among the basin States.For that reason, Vijay argued that the proposed Mekedatu project “cannot be evaluated merely as an engineering proposal.”“Its legal permissibility must first be examined” in the context of the Tribunal Award, the Supreme Court’s 2018 judgment and “the rights of the lower riparian States,” he wrote.The Chief Minister also pointed out that the Central Water Commission had returned Karnataka’s Detailed Project Report submitted in 2019 for revision to ensure compliance with the Tribunal Award and applicable guidelines.Story continues below this ad“This itself demonstrates that compliance with the Award remains an indispensable precondition,” the letter said.Seeks 3 safeguardsBased on these legal arguments, Vijay urged the Prime Minister to ensure that the parliamentary reply be withdrawn and requested that the Union government ensure three safeguards before considering the project further.He sought an assurance that no statutory or administrative approval would be granted unless the project is shown to be consistent with the Tribunal Award and the Supreme Court judgment; that the rights of downstream States over both the quantity and regulated pattern of water releases are fully protected; and that any future consideration of the project be preceded by a comprehensive technical and legal examination addressing the concerns of all lower riparian States.In one of the letter’s most evocative passages, Vijay moved beyond legal citations to the human consequences of the dispute.Story continues below this ad“The River Cauvery is not merely a source of water but the lifeline of millions of farmers and citizens across southern India,” he wrote. “Protecting the integrity of the Tribunal Award and the judgment of the Hon’ble Supreme Court is essential for maintaining confidence in the constitutional mechanism governing inter-State rivers.”He concluded by seeking the Prime Minister’s intervention “in the larger interest of justice, federal harmony and faithful implementation of judicial decisions.”The timing of the letter is notable. Only days earlier, Vijay had proposed meeting Karnataka Chief Minister Shivakumar to discuss the immediate release of Cauvery waters during the current distress season. That initiative drew criticism from opposition parties and some farmer organisations in Tamil Nadu, who argued that bilateral negotiations should not dilute the authority of the Cauvery Water Management Authority or reopen settled legal questions.