When India's rivers link, species follow, and biodiversity may take a new turn

Freshwater ecosystems cover only 2.4% of the Earth's surface but support nearly 10% of all known animal species, including half of all fish species and one-third of vertebrates. They sustain nutrient cycling, climate regulation, food security, livelihoods and water supplies for millions of people. Yet these ecosystems are among the most threatened globally. Water pollution, dam construction, water diversion, invasive alien species (IAS) and overharvesting contribute to their degradation. Land use change, climate change and population growth further intensify these pressures.

The combined effects of river interlinking and biological invasions remain relatively unexplored in environmental research and policy. A study titled River interlinking and biodiversity risks in Indian freshwater ecosystems, by Aravind Neelavar Ananthram, Gokulpriya Raja, M Nobinraja and G Ravikanth, published in Nature Scientific Reports, examines these potential effects across India’s river basins.

The researchers modelled the distribution of 15 naturalised freshwater invasive alien species using bioclimatic variables. They then compared the resulting maps with data on freshwater biodiversity, threatened species and the proposed river linking network. India's proposed river linking projects could connect previously isolated freshwater ecosystems, creating pathways for invasive species to spread and placing native biodiversity at risk.

River interlinking and invasive species: An overlooked risk

Invasive alien species are organisms introduced outside their natural range that can establish themselves and threaten native species and ecosystems. In freshwater habitats, they can compete with native species, alter food chains, degrade habitats, deplete oxygen and cause socioeconomic losses.

Inter basin water transfer projects, which move water between river basins through canals, tunnels or pipelines, can increase the risk of such invasions by changing hydrological connectivity. When previously isolated river systems become connected, species can move into habitats where they did not previously occur.

Despite these ecological implications, the combined effects of invasive species and river interlinking remain largely unexplored in research and environmental policy.

India's National River Linking Project and its ecological implications

India's National River Linking Project (NRLP) is among the world's most ambitious hydrological schemes. It proposes connecting 37 major rivers through 30 links, covering approximately 15,000 km of canals and involving more than 3,000 reservoirs. The project aims to transfer around 174 billion cubic metres of water from surplus to deficit basins and generate 34,000 MW of hydroelectric power.

Its objectives include improving agricultural productivity and reducing flood and drought risks in surplus and arid regions. However, India's river basins have evolved over long periods and are often geographically isolated. These barriers have helped sustain endemic species, which are found naturally only in particular regions. Large-scale canal connections could weaken these barriers, allowing species to move between basins and potentially enabling dominant invasive species to outcompete native populations.

Even a single connection can affect an ecosystem, while a sequence of links could cumulatively increase the movement of non-native species. This could threaten locally adapted species such as the golden mahseer (Tor putitora), which depends on specific temperature and flow conditions for reproduction.

Where are freshwater invasive species concentrated?

The study examined 15 invasive alien species recorded in India's freshwater habitats: eight fish species, four plants, two molluscs and one reptile. These species were introduced for ornamental purposes, aquarium and pet trade, biocontrol or aquaculture. Ten originated in North or South America, while the others came from Europe, Central Asia, China and Africa.

The table below gives the type and country of origin of  IAS.

Table adapted from: Ananthram, A.N., Raja, G., Nobinraja, M. et al.(2026) River interlinking and biodiversity risks in Indian freshwater ecosystems. Sci entific Reports 16, 17552, p 2.

The analysis found high invasive alien species richness across northeastern Indian basins. The Brahmaputra sub-basin, the Ganga and Lower Ganga sub-basins, and the Krishna basin recorded the highest numbers of invasive species.

Biodiversity hotspots are already under pressure

India's river basins support distinctive freshwater communities, but their biodiversity is unevenly distributed. The South Western Ghats and Kaveri basins have the greatest species richness, while the Brahmaputra and Ganga systems also support substantial diversity.

These regions also contain many threatened species. The South Western Ghats and Kaveri are particularly important because they combine high species richness with high levels of threat. The Krishna and Brahmaputra basins also have unusually high numbers of threatened species, even where overall diversity is comparatively lower.

The study reports 1,533 species in the South Western Ghats and more than 1,352 in the Kaveri basin. The Lower Ganga and Krishna sub-basins also support exceptionally high freshwater diversity, exceeding 1,200 species, alongside populations of more than 440 million and 66 million people, respectively. The overlap between biodiversity and threat makes these river systems important conservation priorities.

Biodiversity-rich basins may be more vulnerable to invasion

The study found that river basins with greater native species richness tended to have more invasive alien species. This relationship was particularly relevant to fish, reptiles, mammals and insects, while it was weaker for amphibians and crustaceans.

The findings suggest that biodiversity-rich ecosystems can face a dual challenge: supporting many native species while also providing suitable conditions for invasive species. This makes monitoring and conservation especially important in these areas.

The researchers identified northeastern and peninsular Indian basins as highly vulnerable to the potential impacts of river interlinking compared with central and northern west-flowing basins. Northern and northwestern basins were relatively less vulnerable, with lower invasive species richness and biodiversity.

However, low species richness does not necessarily mean low conservation value. Arid and seasonal basins, including those in Jaisalmer, Bikaner and Barmer, as well as the Indus and Sabarmati systems, may contain rare, endemic and evolutionarily distinct species that remain vulnerable to disturbance.

How proposed river links could spread invasive species

Hydrological connections between basins could allow invasive species to move from areas with high invasion risk into areas with moderate risk. The study estimates that 1,533,480.99 sq km of river basin area faces high invasion risk, 1,286,409.19 sq km faces moderate risk and 610,446.96 sq km faces low risk.

The peninsular component of the NRLP, which proposes links connecting the Godavari, Krishna, Pennar and Kaveri rivers, falls within the high risk category. These connections could increase the likelihood of invasive species spreading towards southern India, including from the Krishna towards the Kaveri and Godavari systems.

The proposed Himalayan component connecting the Ganga, Damodar, Subarnarekha and Mahanadi systems is another ecologically sensitive route. The Lower Ganga, which already has a high invasive species burden, could become a source of invasions into the Mahanadi. This could place the Mahanadi's diverse and already threatened freshwater populations at further risk.

The South Western Ghats emerged as the highest priority basin for conservation because of its high species richness, exceptionally high number of threatened species, substantial invasive species presence and moderate to large basin area. The Krishna, Lower Ganga and Brahmaputra basin complex also require targeted monitoring.

Beyond invasive species: Wider ecological consequences

The risks associated with river interlinking extend beyond biological invasions. Interbasin water transfers can alter river flows, sediment transport and geomorphological processes. These changes may degrade habitats, obstruct fish migration, contribute to heavy metal and industrial pollution, promote biotic homogenisation, reduce ecosystem resilience and facilitate the spread of aquatic pathogens.

Because India's rivers cross national boundaries, the effects of the NRLP could also extend to downstream countries. Climate change may compound these risks. Changes in temperature, precipitation, river flows, sediment regimes and water quality can create new ecological conditions that favour invasive species while weakening the resilience of native populations.

Integrating biodiversity into river planning

India's river linking proposals seek to address water distribution, agricultural productivity and flood and drought risks. However, the study argues that changes in hydrological connectivity could also affect the movement of invasive species and the survival of native freshwater life. This could negatively affect the health and ecological balance of freshwater ecosystems and threaten livelihoods, the very objectives that the plans aim at achieving.

The findings urge decision makers to consider invasion ecology, biodiversity assessments and safeguards, identify vulnerable basins, monitor invasive species and account for ecological connections between rivers while planning for river interlinking projects.

Balancing water management objectives with the ecological needs of river systems is essential to protecting the species, habitats and livelihoods that depend on freshwater ecosystems. The study warns that the very survival of rivers can be at stake while decisions are being made about river linking plans without factoring in their impacts on biodiversity.