Emergency crews pumping water from a reservoir above Whaley Bridge have reached their target.
The Canal and River Trust said it needed to drop the water level by eight metres and confirmed it was down 8.4m.
More than 1,500 people were evacuated from their homes on Thursday amid fears a damaged dam could lead the 300-million-gallon Toddbrook Reservoir to flood the town.
They hope to find out later when they can return.
The trust said: "The water has been pumped out at a controlled rate and good progress is being made."
It said "all safety implications will be assessed" before a decision is made with police about what happens next..
The reservoir is at 25% of its holding capacity.
Authorities are expected to carry out more inspections ahead of a public meeting at 17:00 BST.
Rosie Marshall-Shield is one of the residents hoping to be allowed back home after being evacuated on Thursday.
She went back briefly on Saturday morning after residents were allowed 15 minutes to go back in and grab essentials.
"It was heart-breaking, 15 minutes just to run into your house, just throwing stuff in like a few pairs of underpants and socks," she said.
"I did take a video of the house at the front, just in case it was the last time we were going to come to the house."
Fire crews have been using 23 high-volume pumps to remove the reservoir's water since part of its spillway collapsed on Thursday following heavy rainfall.
The dam wall has been packed with 530 tonnes of aggregate, which is being cemented into place to reinforce the spillway.
Earlier, Derbyshire's Deputy Chief Fire Officer, Gavin Tomlinson, said they hoped to have "some good news" for residents once water levels were down by 8m.
"That will allow the specialists to come in to assess the damage and they will provide the advice for somebody to make the decision with regards to the residents," he said.
"Fingers crossed for them because they have been ever so patient, and hopefully we can give them some good news later. But we will have to wait and see."
The fire service said it had used miles of pipes to remove the water and engineers had built two roads to allow the pumps to be moved closer to the site.
The Environment Agency is monitoring the River Goyt, where the water removed from the reservoir is being taken.
Police have criticised about 20 residents who stayed in their homes within the evacuation zone, saying they were "taking their lives into their own hands" and jeopardising the safety of the emergency services.
Deputy Chief Constable Rachel Swann said: "We will repeatedly visit these people to remind them of the risks they are posing to themselves and emergency responders, however there is no specific legislation under which we can force these people to leave."
Wing Cdr Gary Lane, from the RAF, said a Chinook helicopter was back on Tuesday to drop more aggregate on the advice of civil engineers. Crews are expected to drop a further 200 tonnes on to the spillway.
The Canal and River Trust, which owns the dam, said it carried out an annual inspection of the structure in November and it was "absolutely fine".
The government has said it is considering a national review into the structural safety of dams across the country.