Work is ongoing into the weekend to secure a damaged dam wall at Toddbrook Reservoir.
Over 1,000 residents in Whaley Bridge have been evacuated from their homes due to the "substantial threat to life" posed by the 180-year-old reservoir, which holds 1.3 million tonnes of water.
A severe flood warning remains in force for the area. The Met Office has also warned of further bad weather to come, issuing a yellow weather alert for thunderstorms and possible flooding on Sunday.
Many roads in and around the area have been closed and rail services between Buxton and Hazel Grove, and through the Hope Valley towards Sheffield, are suspended.
As part of a major national, multi-agency response, work began on Friday, with the aid of an RAF Chinook helicopter and 400 tonnes of aggregate, to reinforce the damaged dam wall, stop water from entering the reservoir and reduce the level in the reservoir.
Speaking at a press conference at Buxton's Devonshire Dome on Friday evening, Kem Mehmet, Assistant Chief Constable of Derbyshire Constabulary, said the situation remained critical.
"We have had fantastic support from across the country," he said. "Ten pumps from the fire service are at the scene, and further pumps are being installed throughout the day and evening.
"By doing this we have lowered the water level by half a metre, and further pumps are en-route to help lower the level of the dam.
"I must stress that the structural integrity of the dam wall is still at a critical level and there is still a substantial threat to life should the dam wall fail."
Julie Sharman, chief operating officer for Canal and River Trust, said the water level needed to be reduced by "several more" metres.
Police have said evacuated residents could be away from their homes "for several days", but that it would be allowing one person from each household to access their property to collect essential items and family pets.
This would be carried out under "controlled conditions" for a brief period of 15 minutes.
An evacuation centre remains open at Chapel-en-le-Frith Leisure Centre, and a helpline has been set up by Derbyshire County Council for affected residents. The number is 01629 533 190 and it will be manned between 9am and 10pm.
ACC Mehmet said asking people to leave their homes had been "a really difficult decision", especially in relation to animal welfare.
Gavin Tomlinson, Deputy Chief Fire Officer for Derbyshire Fire and Rescue Service, also praised the support of residents who were asked to leave.
He said: "When they evacuated at short notice, they did so without any complaints, they listened to the advice that was given, and it has made our job much easier because it has allowed us to concentrate on the dam and the emergency instead of other issues."
He said around 150 firefighters were working on the site, supported by a range of other agencies. The ten high volume pumps were removing around 70,000 litres of water a minute from the reservoir, while a number of larger pumps were also in the process of being installed.
Prime Minister Boris Johnson visited Chapel-en-le-Frith and Whaley Bridge on Friday evening to speak to affected residents and thank the emergency service and military personnel who are working to avert a disaster.
Mr Johnson said everything was being done to ensure homes and businesses were protected.
"There is still a substantial risk, and that's why I really wanted to congratulate the emergency services because this is a major problem.
"If that dam goes, you know the potential destruction that can wreak on the whole of the village below, on livelihoods, on families, on homes. That's why it is so important everybody listens to the authorities.
"There's a major, major structural problem with the dam. What needs to happen now is that the water all needs to come out. There needs to be a proper repair - rebuild - of that dam. And that's obviously what we are going to do."
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