Queensland's Environment Minister says the deaths of thousands of fish in the flooded Fitzroy River in central Queensland were due to natural causes.
Property owners found the fish at South Yaamba near Rockhampton, while deaths have also been reported in the Fitzroy River close to the CBD.
Andrew Powell says the deaths were caused by the floods.
"What we've found initially is that there are very low levels of oxygen in the river," he said.
"What happens in a natural disaster is a whole lot of rubbish, vegetation, trees, leaves, carcasses end up in the river as well as sediment, and what happens, reduces the level of oxygen, low levels of oxygen mean fish can't breathe, fish not breathing mean that they die."
Mr Powell says water releases from coal mines are not responsible for the deaths.
"What we have seen is some five-and-a-half million megalitres of water go past Rockhampton since January the 24th," he said.
"That's 11 times the volume of Sydney Harbour [and] of that, less than 10,000 megalitres has come from mines.
"That's less than zero-point-one-eight per-cent."
However Opposition spokeswoman Jackie Trad says an independent inquiry is needed.
"It is not enough to claim without evidence, without scientific proof that this is the cause and not something else that has occurred at the same time," she said.
"The people of Rockhampton, the farmers in the region, need to absolutely rule out that mine water has been responsible for all of these fish deaths."
South Yaamba property owner Bruce Meehan says he has never seen so many dead fish, and it's unusual to find them in a flooding river.
"Obviously we got cattle and we bath in it and irrigate our crops with it so there's something wrong with it obviously", he said.
"I've only been here for three years for three floods but this is the first time but I've seen heaps of floods and never a fish kill like that anyway."
Mr Meehan says he is concerned how it will impact his business.
"The lucerne doesn't do as good if the water is contaminated and we've got to get all our cattle out of this side because they can't drink that water or if they start eating those fish frames, you can start to get a bit of botulism or they can get a bit crook," he said.
© ABC 2013
12:52 EST A thick northwest cloudband has brought the best rain in over a year to parts of inland South Australia.