From hilsa to mahaseer: How dams are emptying India’s rivers of fish

By A  Representative 

On World Fisheries Day 2025, the South Asia Network on Dams, Rivers and People (SANDRP) released a damning compilation of reports that spotlight the devastating toll of dams and river obstruction projects on India’s freshwater fish species and the millions of fisherfolk who depend on them for survival. According to the network, the damming of free-flowing rivers has emerged as the single largest driver of aquatic biodiversity collapse in the country, chiefly by blocking ancient fish migration routes that many species need to spawn and survive.

Iconic species such as the hilsa in the Ganga and the golden mahaseer in the Narmada have suffered catastrophic declines directly linked to large barrages and dams. The Farakka Barrage on the Ganga, which marked its 50th year of operation in April 2025, is facing renewed calls for an independent review and possible decommissioning. Studies cited by SANDRP and the Central Inland Fisheries Research Institute (CIFRI) show that hilsa landings upstream of Farakka have fallen by up to 92 percent, effectively wiping out the upstream fishery in Bihar and Uttar Pradesh. Fisherfolk livelihoods have collapsed, while downstream Bangladesh continues to protest the barrage’s role in altering flows, increasing floods upstream, and accelerating bank erosion in West Bengal.

In the Yamuna, once home to diverse native carp species, exotic invasive fish such as Thai magur and tilapia now dominate the catch. A July 2025 report submitted to the National Green Tribunal by the fisheries department explicitly blamed dam construction, chronic pollution, and blocked migration routes for the near-disappearance of indigenous species, including the complete extinction of hilsa from the Prayagraj stretch since 2010.

Further upstream in the Himalayan states, the National Green Tribunal issued notices in November 2024 to the Centre, Uttarakhand, Himachal Pradesh, and several private hydropower companies over continuing damage to the endangered golden mahaseer’s habitat. Despite the tribunal describing the issue as a “substantial” violation of environmental laws, only one private company had responded by October 2025, leaving the case in limbo.

Recurring ecological disasters linked to hydropower operations continue to shock riverine communities. In Arunachal Pradesh, the 405 MW Ranganadi project triggered yet another episode of mass fish kills in 2025 when maintenance flushing turned the river black with toxic silt, prompting the state human rights commission to order an inquiry. Similar complaints emerged from Himachal Pradesh, where the Barot and Shanan projects released toxic silt into the Uhl and Beas rivers, killing trout during the breeding season and contaminating drinking water sources for Mandi town. The Himachal Pradesh High Court has taken suo motu cognisance and sought reports by March 2025.

Global studies cited in the SANDRP overview paint an even bleaker picture. More than 60 percent of the world’s rivers are now dammed or diverted, with Asia’s Mekong offered as a cautionary tale of a once-thriving fishery fragmented into collapse. A separate peer-reviewed study revealed that oxygen consumption in inland waters has doubled since 1900, driven far more by large dams and nutrient pollution than by climate warming alone. Reservoirs trap organic matter, prolong water residence time, and create vast low-oxygen dead zones that suffocate aquatic life.

From the shrinking paradise of the Indus Delta in Pakistan, where mangrove forests and fishing seasons are vanishing as upstream dams starve the river of freshwater, to the glacial lake outburst flood that reshaped Sikkim’s Teesta in October 2023 and destroyed snow trout spawning grounds, the reports underline a common thread: large hydraulic interventions are pushing a quarter of all assessed freshwater species toward extinction.

SANDRP warned that without urgent policy reversal, including independent post-facto appraisals of aging mega-dams, stricter regulation of silt flushing, and enforceable fish passage mandates, India risks losing its remaining riverine fisheries and the food security of some of its most marginalised communities. The network called the current trajectory “an unacknowledged national emergency quietly unfolding beneath the surface of our rivers.”