By Barasha Das
Loktak lake is northeast India’s largest freshwater wetland and is the ecological heart of Manipur. The lake spans about 287 square kilometres, about half the size of the capital Imphal, and is already under growing stress from pollution, altered hydrology and catchment degradation. Now, a new study warns that climate change could further reduce the fish habitat that sustains livelihoods and food systems.
The study published in the journal Ecological Indicators finds that rising temperatures and shifting monsoon patterns could reduce habitat suitability for native fish species. Using predictive methods, researchers have mapped out how a changing climate will fundamentally alter the lake’s water depth, temperature, and oxygen levels.
Loktak is an indelible part of the Manipuri identity — lives, lore, legends, history, and aquatic ecosystems. It was designated a Ramsar site in 1990, and made its way into the Montreux Record, a register of wetlands that face significant ecological threats, in 1993.
Fish habitat under threat
“We wanted to gauge the health of the entire lake,” says Vicky Anand, lead author of the study. “Fish are considered the most sensitive indicator of a water body’s health. We bypassed harder pollution-tolerant fish that can survive anywhere, choosing instead the rohu (Labeo rohita), an indigenous carp, specifically focusing on the vulnerable juveniles during the critical June-July monsoon breeding period.” Rohu are sensitive to the water quality (WQ) so they’re used as an indicator species, he notes.
Of Loktak’s entire area, only 9 sq. km. is currently classified as a very highly suitable rohu habitat, while around 51 sq. km. falls within the high-suitability category. Another 80 sq. km. falls under the medium-suitability category.
The study projects that even under the Intergovernmental Panel on Climate Change’s (IPCC) low-emission scenario, rohu’s habitat quality will deteriorate during 2041-2060. While areas that are of low suitability to the rohu are expected to expand to 26 sq. km. from around 15 sq. km., high-suitability areas could shrink from 51 sq. km. to just about 15 sq. km.
And under the high-emission “fossil-fueled development” scenario, the decline is far more severe. By the 2050s, nearly 79 sq. km. of the lake is projected to become a low-suitability rohu habitat, while high-suitability areas could contract by about 30 sq. km. from the current levels. At such rates, the decline in habitat suitability would be even more pronounced by the end of the century.
While rohu serves as the benchmark species, more sensitive fish species, including indigenous species, are likely to be affected to an even greater extent, Anand explained.
Manipur produces about 37,125 metric tonnes of fish annually against an estimated demand of 55,000 metric tonnes. Loktak lake and its adjoining catchments contribute to about half this supply.
A transformed wetland
Loktak lake, locally known as Loktak pat, forms the core of the Loktak Wetland Complex, accounting for about 61% of its area, alongside around 20 other wetlands. Historically, these wetlands expanded and contracted with seasonal floods.
This natural cycle has changed with the construction of the Ithai Barrage by the National Hydroelectric Power Corporation, which maintains water levels at around 768 metres above the mean sea level for hydropower generation. This in turn altered the lake’s hydrology and expanded the wetland complex from about 340 sq. km. in 1970 to 469 sq. km. by 2002.
“Loktak (lake) now sits at the receiving end of a vast drainage network, having a catchment area of 5,020 sq km,” says Anand. “Rivers such as the Nambul and Nambol flow directly into the lake; many eastern and western tributaries such as Imphal, Iril and Thoubal first join the Manipur river before feeding the wetland complex.”
The Manipur river flows south into the Chindwin river system in Myanmar. “In practical terms, runoff, sediment and pollutants from across the valley are funnelled into Loktak, linking its health to activities throughout the entire basin,” he adds.
Climate and ecological shifts
According to Global Climate Model (GCM) simulation data, used to project long-term climate trends, the annual mean temperatures are projected to rise by 0.45°C to 1.7°C by the 2050s, depending on future greenhouse gas emissions, the study notes.
To understand the impact of climate change, the researchers compared future climate projections with conditions recorded between 1999 and 2022. “We divided Loktak into a deeper core zone with water depths exceeding 1.5 metres and a shallow shoreline zone of 1.5 metres or less,” says Anand. They found that the shallow shoreline areas are more vulnerable to climate change and already largely fall within the low to medium suitability category for rohu habitat.
A delayed onset of the monsoon, from mid-May to mid-June, is extending the warming period. “The prolonged warming can lead to stratification, where warmer, oxygen-rich water remains near the surface, while cooler bottom waters become increasingly isolated,” Anand adds. “Such conditions can lower dissolved oxygen levels, and accelerate eutrophication, triggering algal blooms, thus creating unfavourable conditions for fish and other aquatic life.”
Bakimchandra Oinam of the National Institute of Technology Manipur and co-author of the study said the ecological changes are already visible. “In my lifetime, I have seen Loktak transform from a largely natural wetland into a heavily regulated system.”
Several indigenous fish species have declined sharply, including pengba (Osteobrama belangeri), Manipur’s state fish. “Older residents of Karang Island (an island within the lake) recall a time when pengba and several other native fish species migrated between the Chindwin basin and Manipur waters. These migrations were annual events at least until the 1970s. Today, finding indigenous fish in local markets has become increasingly difficult, with much of the fish sold as local now being hatchery-bred rather than caught from the wild.”
Many fish species breed beneath phumdi, the floating masses of vegetation, soil and organic matter. “Before the barrage, these followed a natural cycle of floating and settling, drawing nutrients from the lakebed,” Oinam said. Now, the cycle has been disrupted. “Phumdi proliferation, coupled with nutrient build-up, has altered water quality and contributed to significant changes in the lake’s ecology over the decades,” he adds.
The proliferation of phumdi(s) has also been linked to the rapid expansion of athaphum fishing, a traditional practice in which circular fishing enclosures are constructed from thick phumdi biomass.
Remote-sensing analyses show that the area under phumdi in the Loktak wetland increased from about 116 sq. km. to around 134 sq. km. between 1989 and 2002.
“There have been calls to remove the Ithai Barrage, but the structure has regulated water levels for more than three decades,” Anand explains. During this time, the lake’s ecology has adjusted to these altered conditions. “Restoring the original hydrological regime may not automatically restore the ecosystem to its former state and could create new ecological challenges. What is clear, however, is that suitable habitat for fish is shrinking, making timely intervention increasingly important,” he adds.
Restoration amid restrictions
While climate change is an emerging concern, long-standing pressures such as pollution, encroachment and alterations to the lake’s hydrology, exist. “Addressing these issues remains critical for improving the health and resilience of the Wetland Complex,” said Brajakumar Singh, director of the environment and climate change department of Manipur.
Nambul is one of the principal rivers carrying pollutants into the lake. The Manipur government launched the Rejuvenation and Conservation of Nambul River project in 2019 under the National River Conservation Plan of the Ministry of Environment, Forest and Climate Change. The project aims to improve river water quality by intercepting and treating urban wastewater through MBBR (Moving Bed Bio Reactor)-based treatment plants with a combined treatment capacity of 17 million litres per day.
In its 2025 assessment , the Central Pollution Control Board (CPCB) reclassified the Nambul river from Priority-II to Priority-V, indicating an improvement in water quality. CPCB rankings are based primarily on biochemical oxygen demand (BOD), with Priority-I denoting the most polluted stretches and Priority-V the least polluted among those requiring restoration.
According to the Department of Environment and Climate Change’s administrative report 2025–2026, efforts are ongoing to improve the health of the Loktak basin through river conservation and pollution-control measures, regular water-quality monitoring, and wetland conservation programmes carried out in coordination with other agencies.
“We are assessing methane emissions, carbon sequestration potential and land-use changes in and around the Loktak basin,” says Brajakumar. “However, interventions within the Loktak Wetland Complex have been constrained by ongoing court restrictions on development activities. Our department continues to work in the surrounding catchment through measures such as solid-waste management, pollution control and community awareness programmes.”
Judicial scrutiny of development activities in Loktak began in 2019 when the Manipur High Court, in a suo motu Public Interest Litigation (PIL) on Loktak conservation, directed that no new development or construction activities be undertaken in and around Loktak lake without the court’s permission. The restriction was reaffirmed in 2022.
Following the approval of the Integrated Management Plan (IMP) by the Union environment ministry in 2024, the Loktak Development Authority (LDA) approached the High Court seeking permission to implement the plan. In March 2026, the court allowed several approved components of the IMP to proceed under continued judicial supervision, including regular progress and expenditure reports, marking a significant shift from the blanket restrictions imposed since 2019.
“Conservation cannot be achieved through government action alone,” says Moirangthem Asnikumar Singh, an environmental activist and the former chairman of Loktak Development Authority. “It requires a collaborative partnership among government agencies, local communities, experts, civil society organisations, and all stakeholders committed to the well-being of Loktak.”
As climate change intensifies, the future of Loktak lake depends on how effectively these interconnected challenges are addressed across the basin.
This article is republished from Mongabay under a Creative Commons license. Read the original article here.