Origin and Course
The Teesta River is a major transboundary river of the eastern Himalayan region. It originates from the glacial lakes and snowfields of northern Sikkim, particularly the Tso Lhamo region.
The river flows southwards through Sikkim, forming deep valleys and gorges. It passes through the towns of Chungthang, Mangan and Rangpo before entering West Bengal near Sevoke.
In West Bengal, it flows through the districts of Darjeeling, Kalimpong, Jalpaiguri and Cooch Behar. It then enters Bangladesh and joins the Jamuna, the main distributary channel of the Brahmaputra.
The principal course is:
Sikkim → West Bengal → Bangladesh → Jamuna–Brahmaputra system
The Teesta was historically connected with the Ganga system but changed its course following a major flood in the eighteenth century and became a tributary of the Brahmaputra.
Physical Features and Tributaries
The Teesta is a snow-fed and rain-fed river. Its discharge depends on:
- snow and glacier melt;
- monsoon rainfall;
- mountain streams and tributaries.
In its upper course, the river has a steep gradient, rapid flow and narrow valleys. After entering the plains, it becomes wider and develops floodplains, sandbars and braided channels.
Important tributaries include:
- Lachen Chu;
- Lachung Chu;
- Rangit River;
- Rangpo River;
- Great Rangit and Little Rangit streams.
The Lachen Chu and Lachung Chu meet near Chungthang to form the main Teesta channel.
The basin lies in a geologically young and seismically active Himalayan region. It is therefore vulnerable to:
- landslides;
- flash floods;
- riverbank erosion;
- high sediment movement;
- glacial lake outburst floods.
Economic and Ecological Importance
The Teesta supports agriculture, hydropower generation, drinking-water supply, fisheries and local livelihoods in India and Bangladesh.
Its waters are used for irrigating crops such as:
- rice;
- maize;
- jute;
- vegetables;
- tea in adjoining regions.
The steep gradient of the upper river provides substantial hydropower potential. Several dams and run-of-the-river projects have been constructed or planned in Sikkim and West Bengal.
The Teesta Valley also supports rich eastern Himalayan biodiversity. Its forests and riverine habitats contain diverse fish, birds, mammals and plant species.
The river is culturally and economically important for communities living in Sikkim, North Bengal and northern Bangladesh. Tourism, rafting and other recreational activities have also developed along parts of its course.
India–Bangladesh Water Dispute
The Teesta is one of the most important water-sharing issues between India and Bangladesh.
Bangladesh depends heavily on the river for irrigation in its northern districts, particularly during the dry season. India also requires Teesta water for irrigation, drinking-water supply and hydropower development in Sikkim and West Bengal.
The main difficulty arises from the large seasonal variation in river discharge:
- very high flow during the monsoon;
- sharply reduced flow during the dry season.
India and Bangladesh established an ad hoc sharing arrangement in 1983, but a permanent agreement has not been concluded.
A proposed agreement was prepared in 2011, but it could not be signed because of concerns raised by the West Bengal government regarding the availability of water for the state.
The issue demonstrates the importance of Indian federalism in international river agreements because water is primarily a state subject, while treaties with foreign countries are negotiated by the Union Government.
A durable settlement requires:
- reliable data on river flow;
- participation of West Bengal;
- protection of dry-season requirements;
- joint basin management;
- consideration of ecological needs;
- cooperation in flood forecasting and sediment management.
Environmental Challenges
The Teesta basin faces several environmental pressures:
- construction of multiple hydropower projects;
- alteration of natural river flow;
- deforestation and road construction;
- sand and boulder extraction;
- landslides and erosion;
- glacier retreat and changing snowfall;
- unplanned settlements in flood-prone areas.
The South Lhonak glacial lake outburst flood of October 2023 caused a sudden rise in the Teesta and severe destruction in Sikkim. It damaged the Teesta III hydropower project, bridges, roads, settlements and military infrastructure.
The event highlighted the growing risks posed by unstable glacial lakes, extreme rainfall and concentrated infrastructure development in fragile Himalayan valleys.
Sustainable management requires:
- monitoring of glacial lakes;
- early-warning systems;
- maintenance of environmental flows;
- cumulative assessment of hydropower projects;
- regulation of construction in floodplains;
- cooperation between India and Bangladesh;
- participation of local communities.
Conclusion
The Teesta River is central to the ecology, economy and geopolitics of the eastern Himalayan region. Its management requires balancing hydropower, irrigation and development with disaster resilience, environmental protection and equitable water sharing between India and Bangladesh.
