Hydropower is one of the world’s oldest and most important renewable energy sources. It generates around 15% of global electricity and plays a major role in decarbonising power systems. Yet, as a new review from Swedish researchers shows, its environmental cost is often overlooked. Dams and reservoirs disrupt rivers, change water flows, alter habitats, and affect the very species that depend on these ecosystems. The challenge is clear: if hydropower is to remain a cornerstone of clean energy, it must also learn to coexist with nature.
The Ecological Toll of Hydropower
Hydropower dams transform flowing rivers into still reservoirs, disrupting fish migration, reshaping riverbeds, and altering temperature and oxygen levels. Entire river communities — from plants and insects to fish, birds, and mammals — are affected. In many regulated rivers, species that once thrived have declined or disappeared. These impacts extend beyond the water: riverbank vegetation and the animals that depend on it also suffer when natural flood cycles are lost.
Towards Smarter Mitigation
The study highlights that while many solutions exist, their effectiveness is not always well understood. Measures such as minimum water flows, fish passages, controlled flooding, and habitat restoration can help restore balance. Adjustments to dam operation — like moderating sudden water releases (hydropeaking) or protecting downstream spawning grounds — are also part of the toolbox. In some cases, dam removal has proven effective, though this is often politically or economically difficult.
The Role of Systematic Monitoring
What makes this work stand out is its call for programmatic, long-term monitoring. By standardising measurements across rivers and ecosystems, researchers and operators can see which measures genuinely work, under what conditions, and how improvements can be scaled up. This shift from fragmented efforts to coordinated programmes could transform how hydropower and ecology are managed side by side.
Important Implications
In the global north, the pressure is on to accelerate renewable energy while protecting biodiversity. Hydropower sits at this intersection. The path forward is not to abandon it, but to refine it. By building ecological safeguards into the very operation of hydropower plants, we can ensure that clean electricity does not come at the expense of healthy rivers.
The message is hopeful: with careful management, hydropower can continue to power homes and industries while sustaining the ecosystems that make rivers the lifeblood of landscapes.
Source
Balancing hydropower production and ecology − ecological impacts, mitigation measures, and programmatic monitoring, Knowl. Manag. Aquat. Ecosyst. Number 426, 2025, 2025-09-23
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