The Himalayan rivers are recognized as a reliable source of water supply in the countries of the Hindu Kush Himalayan (HKH) region. Increasing need for food and energy for the growing population of the HKH region has stimulated water harvesting from the transboundary rivers and triggered water conflict, environmental degradation and socio-economic turmoil among the riparian nations. Teesta is one such mighty trans-Himalayan river flowing through India and Bangladesh and is recognized as a basin where there is increasing tension between these two nations. Due to upstream interventions including barrage, dam and hydropower construction, the lower riparian region of Bangladesh faces acute water stresses, which hamper the agricultural, fisheries and livelihood activities of the river-dependent communities and impede the economic prosperity of the greater north-west region. The study provides a robust outline of the transboundary nexus between India and Bangladesh, and identifies upstream intervention-induced economic loss and ecological deterioration in the lower Teesta basin. To encourage water collaboration between the riparian states, the study estimates the benefit of transboundary co-operation for the larger socio-economic prosperity and environmental sustainability in the Teesta basin of the Himalayan region, which is decidedly applicable to similar basins in the HKH region and the rest of the world.