An Artery Severed
The Farakka Barrage, a 2,245-meter-long structure on the Ganges River, began operating on April 21, 1975. Its main purpose was engineered to be straightforward: divert 40,000 cubic feet of water per second into the Hooghly River to flush silt away from Kolkata's port, keeping it navigable. This massive hydrological intervention had an unintended biological consequence. It erected a near-impenetrable wall against one of the region's most important migratory fish, the Hilsa shad (Tenualosa ilisha).
Hilsa are anadromous, meaning they spend most of their lives in the salt water of the Bay of Bengal but migrate incredible distances upstream into freshwater rivers to spawn. Historically, the Ganges was a primary migration route. Hilsa would travel as far as 1,287 kilometers from the sea, reaching cities like Allahabad and even Agra. The barrage, with its 109 gates, physically blocked this ancient migratory path. The structure effectively severed the biological connection between the river's upper reaches and the sea, sealing the fate of the upstream Hilsa population.
A Fishery Decimated
The ecological fallout was swift and catastrophic for the fishery. In the middle stretch of the Ganges, from Farakka to Prayagraj (formerly Allahabad), Hilsa landings plummeted by between 83% and 99%. Data from Allahabad shows the scale of the collapse: where the Hilsa fishery once yielded 4.86 kg per hectare between 1961 and 1970, it dropped to just 0.23 kg per hectare in the 1980s. Before the barrage, the average annual Hilsa catch near Allahabad was 33 tonnes; after 1975, it fell to just 0.96 tonnes. For communities in Uttar Pradesh and Bihar, an important source of food and income virtually disappeared.
The barrage's design included fish locks, but they proved ineffective. These structures were not suited to the Hilsa's swimming behavior, preventing any meaningful passage upstream. While the diversion of fresh water did increase Hilsa catches downstream in the Hooghly estuary, it was cold comfort for the upstream regions. The Farakka Barrage created an ecological divide: a thriving fishery below the dam and a barren one above it. This single piece of infrastructure shows that altering a river's flow can have lasting impacts on both ecosystems and the human economies that depend on them.