Work to prevent a damaged dam in Derbyshire from bursting is continuing as the Met Office warns of thunderstorms and possible flooding.
Workers have been pumping water out of the 300-million-gallon Toddbrook Reservoir near Whaley Bridge.
Extra pumps are being installed to speed up the work and contractors are putting concrete between bags of ballast placed on the dam wall.
But the risk of collapse remains at a "critical level".
Daniel Greenhalgh from the Canal and River Trust, which owns the reservoir and dam, said 400 bags had been put in the damaged section on Friday, and a further 70 on Saturday.
"But we are not out of the woods yet," he said. "The last estimate was that residents could be out of their homes for seven days yet.
"We need to get the water down so we can properly inspect the damage to the dam."
He defended the maintenance and safety of the structure.
"This dam was inspected regularly, by us and an independent engineer.
"It needs to be remembered there was a huge amount of rain in a short time and this flooded the area."
Some 1,500 residents of Whaley Bridge were evacuated after part of the reservoir's spillway broke away on Thursday following heavy rain.
Police, the Environment Agency, and the Canal and River Trust, which owns the reservoir, have all said there is a "real risk" the dam could collapse and flood the town.
The dam, built in 1831, became damaged after large swathes of the country were battered by heavy rain and floods earlier in the week.
An RAF Chinook helicopter has put 400 tonnes of sandbags on the affected part of the dam in an attempt to shore it up.
The Labour MP for High Peak, Ruth George, said: "It's not [a good weather forecast]. It's going to be a race as to how fast they can pump the water out of the reservoir.
"It fills up very quickly because it has steep-sided hills on either side which run into it.
"We are going to need to know not just why this happened, after an inspection in November, but also whether there will need to be a different design and a whole new dam."
Derbyshire Deputy Chief Fire Officer Gavin Tomlinson said the situation was "absolutely unique" and everyone had been "working till they can't work any more".
"Our aim is still the same; to prevent more water getting into the reservoir and working as hard as we can to make sure the dam wall retains its integrity.
"We will have the Chinooks working today dropping bags of ballast, we have specialist contractors putting concrete grouting between the bags of ballast to bind it together to give it more security."
On Friday night and Saturday morning, evacuated residents were allowed to return briefly to collect pets and essentials.
The controlled operation allowed one resident per household back into their homes for 15 minutes.
People had complained they were made to leave in such a hurry that they had barely anything they needed with them.
BBC reporters at the scene said there was a "steady stream" of people being allowed briefly back home. Police were taking mobile phone numbers in case of emergencies.
Resident Margot Graham said: "We were told it was at our own risk, but it's a calculated risk.
"Things like bricks and mortar and CDs and books can be replaced, but if my grandmother's ring had disappeared into the water, that couldn't be replaced."
A Derbyshire police spokesman said they were keeping a close eye on the empty part of the town
"We would like to reassure residents and business owners that a staffed cordon around Whaley Bridge remains in place where officers are monitoring who goes in and out of the town.
"Officers are in the area and will be carrying out patrols at periods throughout the day.
"We also have a drone in the area which will assist with crime prevention," they said.
Prime Minister Boris Johnson visited on Friday and promised a "major rebuild" of the dam.
In other developments:
- Firefighters using hydraulic pumps managed to reduce the reservoir's water level by half a metre (1ft 8ins) on Friday, although new levels were not confirmed.
- Julie Sharman, from the Canal and River Trust, said it needed to come down "several metres" before it would be considered safe.
- A "handful" of residents had refused to leave their homes, according to police
A helpline for evacuated residents will be operated by Derbyshire County Council from 09:00 BST to 22:00 on Saturday. The number is 01629 533 190.
Although the weather is currently dry, the Met Office has issued a yellow weather warning for thunderstorms starting on Sunday afternoon and continuing into the evening.
It warns there could be damage and disruption from floodwater and lightning strikes.
Railway lines in the Whaley Bridge area have been closed because of the risk of flooding.