The Three Gorges Dam is the world’s largest hydropower station and one of the most consequential infrastructure projects ever built. Spanning the Yangtze River in China’s Hubei Province, it serves five major functions: flood control, electricity generation, river navigation, water supply, and carbon emission reduction. It also comes with serious costs, including the displacement of over 1.3 million people and the near-extinction of several native fish species. Understanding its importance means weighing both sides.
Flood Control on the Yangtze
Flooding along the Yangtze River has killed hundreds of thousands of people over the past century, and flood control was the original justification for the dam. The reservoir stretches roughly 600 kilometers upstream and holds nearly 40 billion cubic meters of water. That enormous buffer protects over 15 million people living in Shanghai and across the lower Yangtze floodplains, shielding almost 15,000 square kilometers of farmland and urban areas from seasonal surges.
Before the dam, catastrophic floods struck the middle and lower Yangtze roughly once a decade. The reservoir can absorb peak floodwaters during the summer monsoon season and release them gradually, flattening the dangerous spikes that historically overwhelmed downstream levees. This single function was considered important enough to justify the project’s $24 billion price tag and 13-year construction timeline, from 1993 to 2006.
Clean Energy at Massive Scale
The dam is part of a six-station cascade of hydropower plants along the Yangtze. In 2024, that cascade set a record by generating 295.9 billion kilowatt-hours of electricity. To put that in perspective, replacing this hydropower with coal-fired plants would release an estimated 100 million tons of carbon dioxide, 2 million tons of sulfur dioxide, and 370,000 tons of nitrogen oxide into the atmosphere each year. It would also add roughly 10,000 tons of carbon monoxide and particulate pollution.
For a country that still depends heavily on coal, this is a significant offset. China’s air quality problems are well documented, and the dam’s output displaces a meaningful share of fossil fuel combustion. The electricity feeds into the national grid and powers industries and cities across central and eastern China.
Transforming Yangtze River Shipping
Before the dam, large cargo ships couldn’t reliably navigate the upper Yangtze. Seasonal water levels dropped too low, and the gorges themselves created dangerous rapids. The reservoir drowned those obstacles, and the result has been a fundamental transformation of commercial shipping on the river.
The dam’s five-tier ship locks have handled more than 2.2 billion tons of cargo since they opened in June 2003. Year-round navigation is now possible along stretches that were previously seasonal or impassable for large vessels. This turned the upper Yangtze into a major commercial artery, connecting inland cities like Chongqing to the global shipping network through downstream ports.
The dam also features the world’s largest ship lift, which works like an elevator for vessels displacing up to 3,000 metric tons of water. A crossing that once took three to four hours through the lock system now takes about 40 minutes via the lift. For passenger ships and smaller cargo vessels, this dramatically cuts transit times and operating costs.
Displacement of 1.3 Million People
The reservoir submerged entire cities, towns, and villages along a 600-kilometer stretch of the Yangtze valley. At least 1.3 million people were forced to relocate, making it one of the largest population displacements for any infrastructure project in history. The relocation happened during a period of rising national unemployment and major economic reforms in China, compounding the disruption for families who lost homes, farmland, and community ties.
Many relocated residents were resettled in newly built towns on higher ground or moved to distant provinces. The socioeconomic impact has been uneven. Some communities received compensation and access to new economic opportunities. Others, particularly rural farmers who lost fertile river-bottom land, struggled to rebuild livelihoods on less productive terrain. Archaeological and cultural sites dating back thousands of years were also lost beneath the rising water.
Ecological Damage to the Yangtze
The dam’s environmental toll has been severe, particularly for migratory fish. Five flagship species that conservation programs specifically targeted for protection, including the Chinese sturgeon, the Chinese paddlefish, and the Yangtze sturgeon, are now on the verge of extinction despite 40 years of rescue efforts. The Chinese paddlefish was officially declared extinct in 2022.
Dams disrupt fish populations in multiple ways. They fragment habitat, block migration routes, alter water temperature and flow patterns, and trap sediment and nutrients behind the wall. For species that depend on seasonal river conditions to trigger spawning, these changes are devastating. The dam has disrupted the full life cycles of Yangtze fish species, creating what researchers describe as “invalid stocks,” populations that can no longer successfully reproduce in the wild, leading to exponential declines.
Sediment trapping is another major issue. The Yangtze historically carried enormous quantities of silt downstream, replenishing wetlands, maintaining riverbanks, and nourishing the river delta near Shanghai. The dam captures much of that sediment in the reservoir, starving downstream ecosystems and accelerating erosion along the lower river and coastline.
Reservoir-Induced Earthquakes
Since the reservoir first filled in May 2003, a notable increase in seismic activity has occurred in the surrounding area. These are classified as reservoir-induced earthquakes, triggered by the sheer weight of water pressing down on underground rock formations and by water infiltrating cracks, raising pore pressure in the bedrock. The largest recorded event was a magnitude 5.1 earthquake near Badong in December 2013.
Most of the seismic events have been micro or small earthquakes caused by karst collapse (the dissolution of limestone formations), mine collapse, bank reformation, and surface-level geological adjustments. Larger earthquakes in the area correlate with existing fault structures. Seismologists expect the region will continue to experience small earthquakes and possibly medium ones up to magnitude 5.5. While none of these pose a serious structural threat to the dam itself, they do affect communities living along the reservoir’s steep banks, where landslides are an ongoing concern.
Drought Relief Has Been Limited
One of the dam’s stated purposes is supplementing downstream water flow during dry seasons. In theory, the reservoir can release stored water when the lower Yangtze drops to dangerously low levels. In practice, the results have been mixed. Hydrological data from monitoring stations at Hankou and Datong, two key points along the middle and lower Yangtze, show that minimum annual water levels haven’t meaningfully improved since the dam began operating. Drought conditions at those stations fluctuate without clear differences from the pre-dam era.
This is partly a distance problem. The dam sits far enough upstream that releases get absorbed, diverted, or diminished before reaching the most drought-vulnerable areas. It is also a competing-priorities problem: the reservoir needs to maintain certain levels for power generation and flood preparedness, which can conflict with the goal of maximizing downstream flow during droughts.
Weighing Costs Against Benefits
The Three Gorges Dam prevents catastrophic flooding, generates clean electricity equivalent to dozens of coal plants, and opened hundreds of kilometers of river to commercial shipping. Those are real, measurable benefits affecting tens of millions of people. The project cost $24 billion and has almost certainly paid for itself through power generation revenue and avoided flood damage.
The costs are equally real. Over a million people lost their homes. Multiple species are heading toward extinction. The river’s ecology has been fundamentally altered in ways that continue to cascade through downstream ecosystems. Seismic risks have increased, and drought relief has underperformed expectations. The Three Gorges Dam is important not because it is a simple success or failure, but because it illustrates, at the largest possible scale, the tradeoffs societies make when they reshape natural systems for human benefit.