A volunteer firefighter who lost his wife and two children in the Lockyer Valley floods says police are preparing to charge him over their deaths.

Danny McGuire was driving a fire truck in Grantham with his wife and three children when they were hit by a wall of water in January.

His wife, daughter and eldest son drowned, but Mr McGuire and his seven-year-old son survived.

Mr McGuire, who is due to give evidence at Queensland's flood inquiry, says he has been told by senior police that he is to be charged over their deaths.

He says he will be charged with driving an emergency vehicle causing death and driving an emergency vehicle without a current licence.

Toowoomba man John Tyson, who also lost a wife and son in the floods that day, says Lockyer Valley residents will not let it happen.

"The guy should be hailed as a national hero for rescuing people and he left his own family till last, so how they can do that to the guy, I think, is absolutely ridiculous," he said.

"I personally will lead a march on the police station in Brisbane.

"I think I will have more than thousands of supporters with me. I just think it is absolutely ridiculous."

Mr McGuire has engaged a top Brisbane lawyer to represent him in the matter.

A police media spokeswoman says police are unable to comment on cases in which charges have not yet been laid.

Last month Mr McGuire claimed he was gagged from speaking out about the management of the disaster.

He said the fire service ordered him to hide in a motel for nearly six weeks after the floods and to not speak to anyone.

"We were hidden in a motel in Toowoomba and my group officer was told to look after me and make sure I didn't get in contact with anyone because we actually asked to have the place evacuated two nights before," he told the ABC before he was set to testify at the flood inquiry.

"It should have been done and they are trying to hit me up by saying I broke rules and regulations by driving fire trucks in the water to save people, but I did save lives."