The Three Gorges Dam is the world’s largest hydroelectric power station, stretching across the Yangtze River in central China’s Hubei province. Standing 181 meters tall and 2,335 meters long, it generates electricity, controls flooding, and enables large ships to navigate deep into China’s interior. It took 14 years to build, cost at least $24 billion, and displaced more than 1.3 million people.
Size and Structure
The dam is a concrete gravity structure, meaning it holds back water through sheer mass rather than an arched design. At roughly 2.3 kilometers from end to end, it’s one of the longest dams ever built. The reservoir behind it holds a total of 39.3 billion cubic meters of water at its normal operating level, creating a lake that stretches nearly 600 kilometers upstream through the famous Three Gorges river canyons that give the project its name.
How Much Power It Produces
The dam’s installed capacity is 22,500 megawatts, spread across 32 main turbines plus two smaller ones for the plant’s own power needs. To put that in perspective, a typical nuclear reactor produces about 1,000 megawatts, so the Three Gorges Dam has the equivalent output of more than 20 nuclear reactors running simultaneously.
The dam is part of a six-station cascade along the Yangtze that collectively generated a record 295.9 terawatt-hours of electricity in 2024. Annual cargo throughput from the dam’s ship locks recently surpassed 150 million metric tons per year, so the facility serves as both a power plant and a critical logistics hub.
Flood Control on the Yangtze
Flooding was one of the original reasons China pursued the project. The Yangtze’s middle and lower reaches have historically been devastated by seasonal floods. The reservoir dedicates 22.15 billion cubic meters specifically to absorbing floodwaters, holding back surges during the rainy season and releasing water gradually afterward.
For floods that occur roughly once per century, the dam’s storage alone is enough to protect downstream communities without activating emergency diversion channels. For rarer events on the scale of a 1,000-year flood, the dam still reduces the peak, but engineers must also route excess water into designated floodplain areas. In an extreme scenario (a flood so large it might occur once in 10,000 years), the combined capacity of the dam and diversion areas would be overwhelmed.
Ship Locks and River Navigation
Before the dam, the upper Yangtze was too shallow and treacherous for large cargo vessels. The reservoir smoothed out rapids and raised water levels, opening the river to bigger ships. To get those ships past the dam itself, engineers built a five-stage ship lock system spanning 6.4 kilometers, including a 1.66-kilometer main lock structure and a 4.8-kilometer approach channel.
There is also a ship lift capable of raising vessels weighing up to 3,000 tons to a height of 113 meters, functioning essentially as an elevator for boats. Over 22 years of operation, the locks have handled a cumulative 2.24 billion tons of cargo, more than 1 million vessel transits, and over 12 million passengers. Annual throughput has grown from 34 million tons in the early years to a peak of 169 million tons.
Construction Timeline and Cost
The idea of damming the Three Gorges dates back to Sun Yat-sen in 1919, but construction didn’t begin until 1994. The project was built in phases: first diverting the river, then pouring the dam and installing turbines, and finally filling the reservoir to its full height. The entire project was completed in 2008.
The official price tag came to about $24 billion, though some outside analysts have estimated the true cost could have been double that figure when accounting for resettlement expenses, environmental remediation, and infrastructure rebuilding in the surrounding region.
Displacement of 1.3 Million People
As the reservoir filled, it submerged entire towns, cities, and farmland along a 600-kilometer stretch of the Yangtze valley. More than 1.3 million residents had to be permanently relocated. The resettlement took place during a period of major economic reform in China, with rising unemployment making it harder for displaced rural communities to reestablish livelihoods. Many were moved to higher ground nearby, while others were resettled in distant provinces. The scale of this displacement remains one of the largest in human history for a single infrastructure project.
Environmental Consequences
The dam fundamentally altered the Yangtze’s ecology. Slowing the river’s flow caused massive amounts of silt to accumulate in the reservoir rather than flowing downstream, depriving the lower Yangtze of the sediment that naturally replenished riverbanks and wetlands. Downstream biodiversity has declined as fish migration routes were blocked and water temperatures and flow patterns changed. Important archaeological sites and ancient monuments were also permanently submerged as the reservoir filled.
The weight of the reservoir water itself has had geological consequences. A study by the China Earthquake Administration found that the dam triggered roughly 3,400 earthquakes between mid-2003 and the end of 2009, along with numerous landslides. That represented a 30-fold increase in local seismic activity compared to before the reservoir was filled. Most of these earthquakes were small, but the steep gorge walls along the reservoir’s edges remain vulnerable to landslides, particularly during periods when water levels fluctuate rapidly.
Why It Still Matters
The Three Gorges Dam produces enormous amounts of carbon-free electricity, protects tens of millions of people from catastrophic flooding, and transformed the upper Yangtze into a major shipping corridor. At the same time, it displaced over a million people, triggered thousands of earthquakes, and permanently altered one of the world’s great river ecosystems. It remains the most vivid example of the tradeoffs that come with engineering on a planetary scale.