Wivenhoe Dam overflows during January's flood.
Southeast Queensland residents may be apprehensive that 25 per cent of Wivenhoe Dam's water will travel downstream later this week, but community representatives have backed the move.
A 290,000 megalitre release to begin next weekend would mitigate further flooding, Natural Resources Minister Stephen Robertson said yesterday.
The second strongest La Nina weather pattern in history prevailing over Queensland made the "very conservative and precautionary" approach necessary, he said.
Ipswich Mayor Paul Pisasale said some people may be concerned the equivalent of one year's drinking supply will be released from the dam.
"I'd rather deal with people complaining about their lawns dying, than see more homes and properties destroyed by floods," he said.
"More people would be nervous if it's still raining and Wivenhoe is still full.
"I'm pleased they're releasing water ... let's be on the safe side and have Wivenhoe Dam used for flood mitigation."
Low-lying roads near Ipswich, such as Colleges Crossing, Savages Crossing and Twin Bridges, were likely to be closed during the release.
Ipswich councillor Paul Tully said it was possible the Moggill Ferry would again have to suspend services as debris rushed down the Brisbane River.
"I'd say there will be a lot of speculation, a lot of concern and apprehension," he said.
"People will be talking. People who use Colleges Crossing will probably be angry.
"The dam release also might bring back some fears that maybe something more in terms of rainfall is being predicted."
Mr Robertson said the Brisbane River would not break its banks as a result of the planned releases.
"There will be no significant downstream impacts," he said.
Seqwater chief executive Peter Borrows said it was too difficult to say whether a 25 per cent release would stop another flood on the scale of those seen in January - but guessed it was "extremely unlikely".
"It would have had to have been a major reduction in the storage to have any impact on a major flood event," he said.
Mr Borrows stood by the management of the dam, saying it went by the book in the face of unprecedented flooding.