I have written about the Chenab's pulses, the sharp surges and sudden troughs that turn a Himalayan river into a regulated instrument. Those pulses are a story about timing: who controls when water arrives, and whether a farmer's warabandi turn will find the channel full or empty. What India is now building in Himachal Pradesh is a different story entirely. It is a story about territory. A tunnel does not manipulate when water arrives. It decides which river system the water belongs to.
At roughly 3,000 metres in Lahaul-Spiti, India is boring an 8.7-kilometre tunnel through the Great Himalayan watershed. When it emerges, it will carry water from the Chandra and Bhaga, the upper tributaries of the Chenab, westwards through a 113-kilometre canal into the Beas basin. The Chenab is a Western River, allocated by the 1960 Indus Waters Treaty to Pakistan. The Beas is an Eastern River, allocated to India. A tunnel that moves water from one place to another does not merely change a river's course. It challenges the Treaty’s central architecture.
The Indus Waters Treaty of 1960 did not divide water by percentage. After nearly a decade of World Bank-facilitated negotiations, it divided entire river systems. The three Eastern Rivers (Sutlej, Beas, and Ravi) went to India for unrestricted use. The three Western Rivers (Indus, Jhelum, and Chenab) went to Pakistan. India's limited rights on the Chenab are explicitly restricted to four narrow uses, each confined, in the Treaty’s own words, to the drainage basin thereof. The Beas basin is not the Chenab's drainage basin. A transfer from one to the other is not a matter of operational interpretation. It is a category the Treaty does not contain.
The Chenab carries roughly 35 million acre-feet of water annually. The proposed Link Canal would divert less than 1 million acre-feet — a tiny fraction. Yet this small volume is structurally significant. The Treaty was never designed around fractions. It was designed around separation. You cannot slightly move a river from one basin to another any more than you can slightly breach a dam. The partition of river systems was the Treaty’s foundation. A tunnel that crosses it is a structural breach, not a marginal one.
What does the Treaty actually permit? Four things: domestic use, non-consumptive use such as navigation, limited irrigation within the same basin, and run-of-river power generation that returns water to the same river. The Chenab–Beas Link Canal is none of these. It is not irrigation within the Chenab basin. It is not power generation returning water to the Chenab. It is not for domestic use. The Link Canal is a fifth category, and the Treaty’s architecture has no door for it.
For sixty-five years, the Indus Waters Treaty endured because both sides accepted a simple proposition: rivers allocated to one basin would remain in that basin, even when politics deteriorated
This is why the Link Canal is different from the pulses I have documented at Marala. Over the past two years, official WAPDA telemetry has recorded sharp hourly oscillations, abrupt troughs, and staircase-like release cycles, signatures of upstream hydropeaking and cascade management. Those disputes concern timing, and timing is difficult to adjudicate because each project may appear compliant while its cumulative operation produces a different outcome. The Link Canal is not difficult to adjudicate. It is a permanent infrastructure that removes water from the Chenab basin entirely. It does not exploit ambiguity. It challenges a fundamental prohibition.
The legal position has been further clarified by the Permanent Court of Arbitration. In June 2025, the Court ruled unanimously that India cannot unilaterally suspend the Treaty; its declaration of abeyance has no legal effect. In August 2025, the Court reaffirmed that India's rights on the Western Rivers are limited exceptions to a general obligation and must be strictly construed. The Chenab–Beas Link Canal raises precisely the question those rulings were intended to address. It is not a run-of-river project operating within the Chenab system. It is an infrastructure designed to move water from one treaty basin to another.
India may argue that the link merely harvests excess monsoon flows that would otherwise be wasted. But the Treaty does not recognise ‘excess’ as a legal category; it recognises basins. Some will argue that India is merely claiming water it has long been entitled to. This misreads the Treaty’s architecture. The foundational rule is that India must let flow all waters of the Western Rivers for Pakistan's use.
The 3.6 million acre-feet storage cap in Annexure E is not a general water allocation waiting to be claimed. It is a narrow exception to the prohibition on storage, strictly regulated by design constraints, filling periods, and downstream release obligations. Even if India developed every acre-foot of storage permitted under Annexure E, the water would remain within the Chenab system and remain subject to the Treaty’s constraints. The Link Canal instead asserts something different: a right to remove water from one treaty basin and deliver it to another. That is a right the Treaty nowhere grants.
I have visited the Marala Headworks in January, during low flows when the gauge was low, and the downstream calls for Rabi wheat watering were high. I have observed irrigation department officers diverting water from one canal circle to another. That is not an abstraction. It is the arithmetic of scarcity that the Treaty was designed to prevent from becoming routine. The Upper Chenab Canal, the Marala Barrage, and the distributaries that reach Faisalabad and beyond were built on a hydraulic commitment that Chenab water would remain in the Chenab basin. The Link Canal breaks that commitment not by changing the river's rhythm, but by changing its address.
If an upstream state can unilaterally reallocate a treaty-protected river to its own basin, no downstream allocation is secure. This is why Pakistan has raised the Treaty’s violation at the United Nations Security Council: not as a bilateral grievance, but as a test of whether international water law survives when a powerful upstream state declares it optional. India has more reason to be cautious than most.
It is itself a downstream riparian on its major rivers, the Brahmaputra and the Sutlej, originating in Tibet, where it has consistently defended the principles of predictability, restraint, and respect for established arrangements. The principle at stake on the Chenab is therefore larger than just the Indian subcontinent. If power alone can override agreed river partitions, then every downstream state has reason for concern. The tunnel is not merely an engineering project. It is a test of whether transboundary water treaties mean what they say.
For sixty-five years, the Indus Waters Treaty endured because both sides accepted a simple proposition: rivers allocated to one basin would remain in that basin, even when politics deteriorated. The Chenab is still flowing. The question now is whether the principle that kept it there will survive.