Large dams are disastrous for freshwater ecosystems. From preventing salmon migrations, to flooding niche river ecosystems, to blocking nutrient-rich sediment from getting downstream, hydropower is a catastrophe for wildlife. Yet currently, hydropower supplies more than half of our renewable energy. Isn’t cutting our dependence on fossil fuels worth the biodiversity cost of new dams?
The problem with that line of thinking is right there in the question. Dwindling biodiversity and rising emissions are not two separate issues: they are inextricably linked. The ecosystem degradation caused by large hydropower doesn’t just accelerate the global decline in freshwater biodiversity. It also displaces communities, undermines sustainable development, and contributes to climate change.
Green hydropower: fact or fiction?
Although often mis-labelled as renewable, hydropower is not actually net zero. In fact, many hydropower projects are responsible for more greenhouse gas emissions than an equivalent coal-power plant.
Dams transform fast-flowing rivers into large, stagnant reservoirs. They flood vast swathes of carbon-storing forests, wetlands, and peat swamps. When the flooded ecosystems rot, they release enormous quantities of methane gas—much as burning fossil fuels for energy releases greenhouse gasses once trapped in organic matter.
Beyond these direct greenhouse gas emissions, dams also prevent river sediment from reaching the ocean. When allowed to reach the ocean, this sediment not only nourishes highly biodiverse river delta ecosystems, but also traps 200 million tonnes of carbon annually. Again, biodiversity loss directly undermines hydropower’s net zero ambitions.
Indeed, the United States and Western Europe are already lessening their dependence on hydropower. Along with its destructive impact on local ecosystems, large hydropower presents a number of logistical challenges that often make it more trouble than it’s worth.
On average, dam construction costs twice as much and takes 50 per cent longer than projections claim—meaning that in reality, it’s just not worth the price. Over time, river sediment clogs dams. The decreased reservoir capacity and damage to machinery severely reduces the amount of energy generated. Climate change and rising water demand means lower river volume, and hence shrinking hydropower capacity.
Inga 3: A case study in destructive hydropower
Yet the global North has proven less willing to apply this knowledge to hydropower investment in less wealthy nations. In the Democratic Republic of the Congo (DRC), the proposed Grand Inga Dam would be the largest hydropower project in the world. The project builds on the legacy of Inga I and II, two dams constructed in the 1970s and 80s. Today, Inga 1 and 2 run at less than 50 per cent capacity because of sediment build-up.
Rather than investing in the maintenance and modernisation of the existing dams, the international finance community and the government of the DRC are pushing for the construction of Inga 3, the next stage in the project. The dam would displace 37,000 people and cost 14 billion dollars (with overshoot nearly inevitable). 90 per cent of Congolese people, who remain disconnected from the national grid, would likely be unable to access the energy it generates.
Instead, most of the power generated by Inga 3 will fuel destructive mining projects or be converted into hydrogen for export, allowing citizens of wealthier nations to benefit from the energy the dam generates while avoiding its negative social and environmental impacts. All for inefficient energy that probably won’t even be ‘low carbon’.
In the DRC, Synchronicity Earth supports CORAP, or the Coalition of Civil Society Organisations for the Monitoring of Reforms and Public Action (CORAP). CORAP advocates for a just energy future in the DRC, with a focus on preventing the construction of Inga 3, and instead prioritising decentralised solar and wind energy for the benefit of the Congolese people, rather than big business or the international market.
CORAP lobbies the government while collaborating with local people—including a group of fishermen who oppose Inga 3 because of the catastrophic impact it would have on freshwater fish populations in the Congo River. These fishermen know that, beyond their greenhouse gas emissions, negative social impacts, and destructive impact on the surrounding environment, large hydropower projects just aren’t worth the freshwater biodiversity cost.
Unprecedented decline: how dams destroy freshwater ecosystems
The fishermen of the Congo River, like many communities around the world, depend on the river’s unique biodiversity to feed their communities and maintain sustainable livelihoods. Around the world, people also rely on freshwater ecosystems for everything from cultural connection and recreation, to water purification and climate regulation.
The abundance of life in freshwater ecosystems declined by 83 per cent between 1970 and 2018, far eclipsing the rate of loss in either terrestrial or marine ecosystems, and hydropower is a primary culprit. Dams disrupt migratory patterns, preventing many fish from reaching breeding grounds or following food as the seasons change. Trapped sediment contains nutrients, starving ecosystems and species downstream of the dam.