Public affairs officer Lisa Coghlan said Thursday that by limiting releases, the 37 billion gallons of flood waters were retained at Lake Lanier.
Northern Georgia has received several feet of rain over three days.
On Thursday President Barack Obama issued a disaster declaration for Georgia, ordering federal aid to assist state and local recovery efforts in the wake of severe storms that caused massive flooding this week.
Vice President Joe Biden was scheduled to survey flood damage today.
Obama's declaration makes federal funding available to affected residents of Cobb, Paulding, Douglas and Cherokee counties. Aid may include grants to help pay for temporary housing, home repairs and other serious disaster-related expenses.
"It's a life-saver," Georgia Insurance Commissioner John Oxendine said of the federal declaration. "It allows people to clean up and restore their homes."
Oxendine said the latest estimate shows more than 10,000 homes with significant flood damage. "That's probably going to go up," he said. "Our initial damage estimate of $250 million, that's a conservative number."
In Cobb County, one of the counties hit hardest by the flood, spokesman Robert Quigley said drinking water was not affected and a sewage plant that was damaged by the storms was again operating.
Most Cobb County schools reopened Thursday, although one school in Austell, a community heavily damaged by the flood, remained closed and many Austell residents were still unable to return.
"We're still waiting for the water to drop some more so people can go back to their homes," Quigley said.
Jim Cash, assistant chief of the state Environmental Protection Division's watershed protection branch, said that so far, there was no evidence of problems with the quality of drinking water.
"Everything on the ground got flushed into streams. Most of it was diluted down pretty well," Cash said.
He said water quality was being monitored, and preliminary results show no serious impact from the floods.
To apply for assistance, residents in the four counties should call FEMA at 1-800-621-FEMA to apply for assistance.