Chinese engineers have demolished the temporary barrier behind the Three Gorges dam, in a spectacular explosion.
The barrier, called a cofferdam, was used to hold back the waters of the Yangtze River while the permanent structure of the dam was built.
Enough explosives to topple 400 10-storey buildings were used in the blast, China's Xinhua news agency said.
The controversial dam - the world's largest hydro-electric project - will not be fully operational until 2009.
When its 26 turbines become operational, the dam will have a capacity of more than 18,000 megawatts.
On 20 May, builders poured the last concrete to complete the construction of the dam's 185m-high (610ft), 2,310m-long (1.4 miles) main wall.
Just three metres of the cofferdam, 100m upstream from the main dam, protruded from the water before the blast, Xinhua said.
Engineers used 191 tonnes of underwater explosives for a demolition operation which took about 12 seconds and caused some 190,000 cubic metres of concrete from the cofferdam to fall into the river.
Its demolition left the main dam holding back the full weight of the river, with water behind the main dam expected to reach a height of 139m.
Chinese officials said the blast would not cause geological damage.
China says the dam, in central Hubei province, 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.
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.