Ichthyologists wanted for dam greenwashing

Dam under construction on Tembat River of Terengganu State, Malaysia.

This river was a biodiverse home to a species of mahseer (Tor tambra) among many other fishes. It feeds into Kenyir Lake, a reservoir shown to have suffered from loss of diversity due to dam building, in an area dominated by an ancient tropical rainforest: Taman Negara National Park.

Lockdown dam development webinars in Himalayan regions have been recruiting fish conservationists as specialist speakers.


Fish passes are being introduced at both new and existing dam projects as a way to make hydropower more sustainable.

My colleagues and I have all been invited to discuss this topic during many regional online discussions. The claim is that “fish passes do make dams green”.

The International Finance Corporation of the World Bank has been a prime mover in organising events to highlight the importance of fish passes. Smaller bodies like Nepal Hydro Lab have also been involved.

Fish passes may make a dam more sustainable than not, but are they truly green just for allowing a strong swimmer like mahseer fish to be able to pass?


Countries like Nepal see sustainable use of their abundant waters as a fast way of developing power for industry. Damming rivers is adopted by politicians and media alike as a sustainable solution for a patchy electricity supply.

International funding bodies line up to offer loans. Politicians use these as a message of inward investment and an opportunity to reduce pressures on countries at most risk through climate breakdown impacts.

Outside agencies push for these countries to achieve sustainable development goals and the adoption of hydropower looks like a simple solution to address multiple issues.


In the latest figures available for India (2019-20), total gross electricity production of 1,383 TWh and consumption of 1,208 KWh clearly shows excess generation. India produces excess capacity and exports to both Nepal and Bangladesh.

Development plans in Nepal use the argument that excess electricity generation can be sold to India. Given that India already produces its own excess and sells surplus to Nepal, how can this be a sustainable economic model?

It is a situation that repeats across the mahseer range countries, with India replaced by Thailand or China and Nepal replaced by Laos or Cambodia.


Not only is there a general, regional excess of production, costs of renewable energy production are falling fast. Hydropower, by comparison is becoming a financially costly method of power generation.

Not only financial costs, the time implications are also better for renewable energies like solar and wind. A typical dam takes five years to build, while comparable capacity of other renewables takes only two to three years.

The concern of most involved in river ecosystem conservation is that many of the ecological costs are ignored in the drive for dam building. Using fish migration to greenwash those concerns is clearly becoming a priority for developers and funders who are losing the economic argument.


Dammed rivers and reservoirs show greatly reduced fish diversity compared to intact river habitat. In a study in northern Malaysia, the numbers of native species were reduced by 40 percent in Lake Kenyir compared to before the dam was built.

Insect populations often shift, away from those with natural ecosystem function in favour of those that carry diseases like malaria and dengue fever. This extra burden on healthcare is not factored into planning calculations.

Aquatic birds, especially those that nest on sands exposed by seasonal flow variation, see eggs and chicks lost to water releases for power generation.

Many vital ecological links are being broken, some with unforeseen consequences. This is true at both local and whole river basin levels.


Aquaculture is another suggested benefit of reservoirs, but escapes of alien species, which are easy to breed, are reality in these countries.

The Asian Development Bank, for instance, suggests breeding the known invasive Chinese silver carp in new reservoirs in Nepal.

When this species, Hypophthalmichthys molitrix, was introduced into India’s Gobindsagar Reservoir on the Beas and Sutlej Rivers, escapees came to dominate the local fish population. Recent monitoring shows it now comprises 85 percent of the entire fish assemblage.


The discussion needs to be shaped to include all the things that need to pass a dam. Or put another way: everything that moves within a river, in any of the four dimensions of connectivity, should be considered.

Prime among them is water flow, with impacts for downstream groundwater recharge. Close behind is sediment transportation.

Change to the sedimentation process is one of the most costly impacts of dam building, yet usually completely ignored in economic analysis.

The effects of losing sediment transportation will be felt along the entire river. Agriculture loses natural fertiliser and delta areas most vulnerable to climate impacts become prey to deadly erosion.


Fish need to be able to reach a dam.

Plans for a run-of-the-river facility on Karnali River in western Nepal will see water diverted into a 1 km tunnel and the river bed virtually dry. Although fish passes are included in the design, they are useless if the fish cannot access them.

For fish like mahseer, migration is an almost constant state of being. They do not simply move, as is commonly believed, once the monsoon rains come. And there are other fish species that migrate to spawn during the lowest water conditions.


Maintaining ecological balance is the critical factor. There are plenty more fish in the river than mahseer. Ensuring these can all complete their life cycles is the only way to maintain habitat integrity.

A fish pass suitable for a mahseer may be an impenetrable barrier for an eel. Small fish that require lateral connectivity to move from shallows to deeps for feeding or spawning will suffer from living in a featureless channel.

Insect larvae need to drift downstream, not get stuck behind a concrete wall. Otters, dolphins, crocodiles and elephants have to move up and down the river as water levels change.


It is time to include the whole picture in any future hydropower development proposal.

Adding a fish pass is not likely to make such an intrusive project sustainable or green.

If that pass is only suitable for a single species, no matter how endangered, the whole system is in peril.

The long term impacts of that peril, both ecological and financial, are faced by some of the most vulnerable, often for short term political gain.

This Author

Steve Lockett is executive director of Mahseer Trust, a non-profit working to conserve Asian rivers and fish for local community and ecological benefit. He tweets at @stevenlockett and @MahseerTrust.