China has completed construction of the main wall of the Three Gorges Dam - the world's largest hydro-electric project.
Builders marked the occasion with a colourful celebration ceremony
The controversial dam in central Hubei province will not be fully operational until 2009, once all its generators are installed.
China says it will provide electricity for its booming economy and help control flooding on the Yangtze River.
Critics say over a million people were moved from the area, and the reservoir behind the dam is already polluted.
On Saturday, builders poured the last amount of concrete to complete the construction of the 185m (607ft) high, 2,309m (1.4 mile) long wall.
A senior Chinese official said the event marked a "landmark progress" in the dam's construction, the state-run Xinhua news agency reported.
"However, tasks such as building of power houses of the dam, the ship lock and shiplift are still formidable," said Pu Haiqing, deputy director of the dam's construction committee.
When its 26 turbines become operational in 2009, the dam will have a capacity of more than 18,000 megawatts.
Already the world's second-largest consumer of oil, China says it needs alternative energy sources to combat widespread power shortages and keep its booming economy powering along.
LARGEST HYDRO-ELECTRIC DAMS
Three Gorges Dam, China - 18,200 megawatts
Itaipu, Brazil/Paraguay - 12,600 megawatts
Guri, Venezuela - 10,000 megawatts
Grand Coulee, US - 6,494 megawatts
Sayano-Shushensk, Russia - 6,400 megawatts
Krasnoyarsk, Russia - 6,000 megawatts
Churchill Falls, Canada - 5,428 megawatts
La Grande, Canada - 5,328 megawatts
Source: International Hydropower Association, UK
The authorities also hope the dam will help control flooding on the Yangtze River, which in the past has claimed hundreds of thousands of lives, the BBC's Quentin Somerville in Shanghai reports.
But campaigners say the dam comes at too high a cost.
Over a million people have been moved from their homes to make way for the project and more than 1,200 towns and villages will disappear under its rising waters.
Environmentalists say the water behind the dam is already heavily polluted.
China says the whole project will cost about $25bn (£13bn), but environmentalists estimate it to be several times higher.
THE THREE GORGES DAM
Type: Concrete Gravity Dam
Cost: Official cost $25bn - actual cost believed to be much higher
Work began: 1993
Due for completion: 2009
Power generation: 26 turbines on left and right sides of dam. Six underground turbines planned for 2010
Power capacity: 18,000 megawatts
Reservoir: 660km long, submerging 632 sq km of land. When fully flooded, water will be 175m above sea level
Navigation: Two-way lock system became operational in 2004. One-step ship elevator due to open in 2009.