The opening of the floodgates of the Ross River dam in Queensland created what Australia's weather bureau called "dangerous and high velocity flows". With the dam at more than 300 percent capacity, engineers said they had no option.
Downstream homes in the coastal city of Townsville are flooded and more than a thousand people have moved to safety and been evacuated from their homes.
In some parts of Townsville, salt-water crocodiles displaced by the floodwaters have been spotted, adding extra risk and danger.
Al Jazeera's Bernard Smith reports.
