Hundreds of people were evacuated from a town in central England as a British military helicopter was called in Friday to prevent a reservoir dam from collapsing.
The Toddbrook Reservoir dam was feared to be on the verge of caving in following heavy rain, threatening the lives and homes of residents in Whaley Bridge.
One side of the dam spillway weakened when the panels started to come away on Thursday.
A Royal Air Force (RAF) helicopter lowered bags of aggregate into the damaged part of the dam wall on Friday, while firefighters, scrambled from around the country, have been pumping water out of the reservoir.
"It is a critical situation," said Julie Sharman, chief operating officer of the Canal and River Trust which runs the reservoir.
She said water levels had reduced by around 20 centimetres overnight.
The British government has issued a "severe flooding - danger to life" warning for the area directly below the dam.
Whaley Bridge in Derbyshire, is on the edge of the Peak District National Park and 26 kilometres southeast of the city of Manchester.
The reservoir dates back to the 19th century.
Fast-flowing water had been rushing over the spillway before the collapse.
"I've lived in Whaley for the best part of 45 years, and I've never seen water flood over the dam like that, ever, nor thought that we could possibly be at risk in this way," said local resident Carolyn Whittle.
The RAF Chinook heavy-lift helicopter was dropping some 400 one-tonne bags of sand, gravel and stone into place.
Derbyshire Police assistant chief constable Kem Mehmet said more than a thousand people had been evacuated from areas that would be flooded immediately if the dam wall failed.
"As there is still a risk the dam will fail, please stay away from the area," he said.
"Being asked to leave your home is an extremely difficult and worrying situation to find yourself in. However, it is not a decision we have taken lightly."
He said "everything humanly possible" was being done "to save the reservoir wall and to protect the town".