RAF crews have dropped more than 100 tonnes of ballast to block a breach in a river bank which caused severe flooding in a town.
The River Steeping burst its banks at Wainfleet All Saints, Lincolnshire, on Wednesday after the equivalent of two months' rain fell in two days.
A state of emergency was declared on Thursday with more than 70 properties flooded and residents evacuated.
Three Chinook helicopters were at the scene on Friday evening.
Ian Reed, the head of emergency planning in Lincolnshire, said: "We're confident that we are definitely seeing a change and, whilst water levels are not going to go down really quickly, it is helping and it's doing exactly what we wanted it to do.
"So, that operation has been a success.
"It's a temporary measure, but it's doing what it set out to achieve."
A firefighter was taken to hospital with minor injuries after he was injured moving equipment overnight on Thursday in Wainfleet.
Assistant Chief Constable Shaun West of Lincolnshire Police said the rescue effort was showing some early signs of success.
"Where there were thousands of gallons of water gushing through that breach when I started, that is starting to stem."
A rest centre for Wainfleet residents was set up in nearby Skegness.
Jean Hart, who has lived in Wainfleet for 40 years, said it was the worst flooding she had ever seen.
"To see our house under water is absolutely horrendous," she said. "The whole of my house is completely devastated."
She said she and her husband Kevin were now at a loss as to what to do.
"[You realise the] things you take for granted," she said.
"It's not just us - so many people are in the same situation and my heart goes out to them."