Hydropower and irrigation dams pose threat to freshwater fish species: Study

  • Experts call for immediate actions to stop further degradation of aquatic resources

Apr 11, 2019-

Hydropower and irrigation dams built to divert water from various rivers of the country are posing a threat to aquatic resources, mainly fish species, according to a latest study.

An Asian Development Bank rapid study that assessed the potential impacts of various hydropower and irrigation dams built along the rivers has concluded that these infrastructure adversely affect both the indigenous as well as migratory fish species in the rivers.

The study evaluated the operation of a number of hydropower and irrigation projects with dams—the Kali Gandaki, Marshyangdi, Middle Marshyangdi, Kulekhani, Khimti and Trishuli hydropower projects, and the Babai irrigation Project—to find whether these constructions had any impact on fish species and their habitat.

“Early findings of this study suggest that fish population in Nepal’s river basins with dams are in a sharp decline,” said Deepak Bahadur Singh, a senior environment officer and co-author of the study.

The study recorded 223 dams at different phases of construction at different locations in the rivers of Nepal. A comparative study of environmental impacts and effectiveness of deployed mitigation measures in 13 dam projects was carried out during the study.  

Various other rivers have also witnessed a decline in the number of fish species including the Golden Mahseer, an iconic fish found in the Himalayan rivers, after the degradation of ecosystem because of human activities.

The researchers have concluded that among the various threats to freshwater biodiversity, artificial obstruction plays an important role as construction of hydropower dams has occurred at an unprecedented rate, disrupting dynamic processes and ecological integrity of natural systems.

The report also pointed out that hydrological alteration by blocking water flow through construction of dams had more adverse impacts on fish species in the river than the pollution and rampant fishing in those rivers.  

Experts have warned that rising number of hydropower projects and dams that will come along in future will further threaten fish species in the country.

“While we are marching towards prosperity with development of hydropower projects, we can still adapt to some measures to protect our rich aquatic resources,” said Singh. “Some technical considerations while building dams or other such projects can go a long way in saving the fish population. Providing a fish ladder, building a fish passage, and a fish bypass channel, are some examples.”

Most of these rivers surveyed during the study had no such measures to maintain the natural flow of water and protecting the fish species dependent on those river ecosystems. Some of these measures were installed in these rivers but they were not in operation, according to the study.

“For example, a fish passage should meet the requirement of the species and can be varied as per the river and species that live in the river-basin,” added Singh.

According to Tek Bahadur Gurung, acting executive director at Nepal Agricultural Research Council, the country needs to prioritise construction of “fish-friendly hydro dams”.

“There will be more dams in future. We cannot stop that, but we can consider protecting aquatic biodiversity,” said Gurung. “We have to use available solutions and technology to protect our fish species while we harness our hydropower potential. As of now even available measures like fish ladder and fish passages are not even working.”

Experts also suggested that adapting compensatory measures like breeding fish in hatcheries and releasing them upstream and downstream of the dam annually to maintain their populations could be effective in maintaining their populations in the river basin.

Amending the existing Aquatic Animal Protection Act, 1960, and other laws, stringent monitoring of dams construction with minimal impacts of biodiversity, declaring certain river basin aquatic conservation area and establishing environment monitoring in each local units are some of the recommendations put forth by the experts involved in the study.

“We hope this study will open the door for more discussion and extensive research on this important topic,” said Mukhtor Khamudkhanov, ADB’s country director for Nepal. “A broader understanding of the importance of a healthy fish habitat to maintaining balance in the ecosystem and food chain and generating economic and social benefits from fisheries will go a long way in promoting environmentally sustainable development.”

Published: 12-04-2019 07:00

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