By Daniel Griffiths
BBC News, Mianyang
China has finally won the battle with a dangerous quake-formed lake after weeks of anxious waiting, averting a potential disaster for hundreds of thousands of people.
The controlled release of the water with no major flooding was exactly the result the authorities wanted.
In the city of Mianyang, one and a half hours downstream from Tangjiashan lake, the river bed is usually wide and water levels low.
Water levels in Mianyang downstream rose after the quake lake was drained
In just a few hours that changed, dramatically.
The waters released from the lake rushed down the valley turning the river into a thick, brown muddy torrent, more than 100m (110 yards) across.
There were trees, bushes and other debris in the water.
There was little chance the river would burst its banks. The authorities, however, were not taking any chances.
Police and soldiers were stationed on the riverbanks.
Large crowds gathered to watch the spectacle, standing along the banks and on the main bridge over the river.
"I'm not frightened," one man said. "The government will see to it that we are safe."
It has not been that simple for the authorities.
There were concerns that aftershocks and bad weather might lead to the lake bursting its banks.
It was formed by a landslide triggered by the earthquake last month.
The level of water behind its banks of mud and rock rose quickly, due in part to heavy rains in the region.
The government moved quickly - the last thing it needed now was another major disaster.
More than 200,000 people were evacuated from their homes.
Soldiers and engineers worked around the clock to dig a sluice to drain away the water.
When that did not work, they used rockets to blast away some of the debris, widening the channel for the lake water.
That method brought success - but at a price.
Much of the town of Beichuan, just below the lake, was flooded by the rushing waters.
Yet Beichuan was already a ghost town - abandoned after being so badly damaged during the earthquake that the authorities decided not to rebuild it.
For some, seeing their old home town under water was too much.
"It's really hard for me to take. Our city was so good and beautiful, but now there's nothing left. My heart aches," said one farmer, speaking to international media.
For the government, this has been a major test.
The story frequently made the headlines in the state-run media.
Political leaders, including Premier Wen Jiabao, have made high-profile visits.
The official strategy has paid off.
The authorities have called the successful draining of the lake a "defining victory".
There are other, smaller quake lakes that may still cause problems.
But the draining of Tangjiashan lake has brought a moment of relief for a nation still coming to terms with last month's devastating earthquake.