Mekedatu reservoir row reignites the Tamil Nadu-Karnataka Cauvery dispute

The long-running dispute over the Mekedatu dam project has flared up again between Tamil Nadu and Karnataka. The Tamil Nadu Assembly passed a unanimous resolution opposing Karnataka's plan to build a drinking water-cum-balancing reservoir across the Cauvery river at Mekedatu, about 100 km from Bengaluru. The project would store 67.16 thousand million cubic feet (TMC ft) of water through a reservoir costing around 9,000 crore rupees, with a 400 MW hydropower component but no irrigation component.

The trigger was Karnataka, the upper riparian state, preparing to submit a revised Detailed Project Report (DPR) after the Supreme Court dismissed Tamil Nadu's petition seeking review of a November 2025 decision. The Court had called Tamil Nadu's challenge 'premature'. The terms 'upper riparian' and 'lower riparian' simply mean the states located upstream (Karnataka) and downstream (Tamil Nadu) along a shared river. In its 2018 Cauvery judgment, the Supreme Court had already allowed Karnataka an extra 4.75 TMC for Bengaluru's drinking water needs.

On paper, a project meant only for Bengaluru's drinking water should not alarm the downstream state. What complicates matters is the deep trust deficit between the two states. Tamil Nadu fears that a large reservoir upstream could let Karnataka control and hold back river flows during dry spells, hurting its farmers in the Cauvery delta who depend on water released from upstream.

This dispute sits within India's framework for resolving inter-state river water conflicts. Such disputes are handled under the Inter-State River Water Disputes Act, 1956, through tribunals such as the Cauvery Water Disputes Tribunal, with the Supreme Court and bodies like the Cauvery Water Management Authority overseeing implementation. It is a classic test of cooperative federalism, where states sharing a river must balance their rights with the larger national interest.

Aspirants should remember the Cauvery basin states (Karnataka, Tamil Nadu, Kerala, Puducherry), the meaning of upper and lower riparian, the Inter-State River Water Disputes Act, 1956, and the role of tribunals versus the Supreme Court. Note the Mekedatu specifics: drinking water and power, no irrigation, 67.16 TMC, near Bengaluru.