Salinity level is increasing in coastal areas due to climate change. The situation is worsened by infrastructure projects, embankments, and severe pollution. As a result, coastal river fish and aquatic species are being threatened. Research indicates that from February to June, salinity levels exceed normal levels in the country’s coastal area, forcing freshwater fish to migrate. Experts warn that these changes are also affecting local communities, altering their livelihoods, health, and dietary habits. The shift in aquatic habitats is closely linked to growing socio-economic instability in coastal regions.

In January, the World Bank’s Development Research Group published a study titled ‘Fishing Climate Change in Coastal Bangladesh: The Economic and Health Impacts of Increasing Salinity.’ The study examined 29 fish species and found that salinity levels rise from early spring until just before the monsoon season. This directly affects riverine fish and other aquatic life. Freshwater fish, unable to tolerate the high salinity, shift their habitat elsewhere, making life difficult for local fishermen. Fish prices increase, while fishermen’s protein intake decreases.

Researchers collected salinity data from five river stations in Khulna, Mongla, Sarankhola, Amtali, and Galachipa between 2020 and 2022. The rivers studied were Rupsa, Pasur, Baleshwar, Payra, and Ramnabad. They analyzed the lowest and highest salinity levels in these rivers throughout the year. The findings show that salinity levels peak from February to June.

According to the research findings, all five stations recorded the highest salinity levels from February to June, which then decreased during the monsoon season. Salinity in water is measured in parts per thousand (ppt). The highest recorded salinity levels were 8.89 ppt in Khulna, 12.75 ppt in Mongla, 1.18 ppt in Sarankhola, 0.23 ppt in Amtali, and 0.58 ppt in Galachipa.

Researchers consider the increase in salinity levels in coastal rivers from February to June a natural phenomenon. During this period, Bangladesh receives little to no rainfall due to seasonal and climatic variations. As a result, upstream water does not have enough volume when reaching the sea, contributing to rising salinity. However, the primary cause is the obstruction of water flow due to dams, including India’s Farakka Barrage and other structures built within Bangladesh. While some water flows through the Meghna estuary, the expected flow from the Padma basin via the Gorai and Kopotakkho rivers has been completely disrupted. The combination of low rainfall and barriers from both domestic and foreign dams causes salinity levels in coastal waters to rise beyond normal during this time.

However, Professor Dr. Md Moniruzzaman, former chairman of the Geography & Environment Department at Jagannath University, argues that pollution plays a bigger role in fish migration than salinity alone. Speaking to Bonik Barta, he said, “Every fish species has a certain tolerance to salinity. The pre-monsoon salinity levels alone wouldn’t be a major threat if upstream water could flow naturally. But severe river and ocean pollution is a bigger problem. Even if fish can tolerate some salinity, the extreme pollution is beyond their capacity. Pollution kills aquatic plants that serve as food for fish, making their habitat unlivable. Some migrate due to food scarcity, while others die from consuming toxic plants. Those that cannot adapt or relocate simply perish.”

Experts also challenge the notion that climate change is the main driver of increasing salinity. Instead, they blame upstream dams and government-built embankments. During high tide, silt carried by seawater fills up river and canal beds. Without regular dredging and fresh water inflow from upstream, high tides push saline water deep into settlements, leaving salt deposits in the soil. Over time, this leads to land degradation, riverbank erosion, and declining crop yields. As rivers and canals become clogged, fish and other aquatic species are forced to relocate. This disruption is also affecting fish breeding. Due to salinity, fish larvae are no longer found in Khulna and Satkhira as they once were. Experts believe this is directly impacting fish reproduction and overall aquatic biodiversity.

The impact extends beyond aquatic life. According to Professor Dr. Abdullah Harun Chowdhury of Khulna University’s Environmental Science Discipline, excessive salinity is reshaping the socio-economic landscape of coastal areas. He told Bonik Barta, “Fish stocks are depleting, forcing fishermen to switch professions. Women and children are facing increased insecurity. Agricultural production is suffering. Child labor and crime rates are rising. Those who once relied on fishing have now shifted to other occupations. In other words, just as fish are changing their habitat due to changing conditions, coastal communities are also being forced to relocate.”