Australia-The big wet and cost to farmers.

AUSTRALIA-After a week of torrential rain in north Queensland, forecasters are warning that areas to the south should brace for possible flooding as the monsoonal trough bears down.

Three people are missing in north Queensland floods, including a five-year-old boy feared taken by a crocodile, as heavy rain continues to pound the region.

Over the weekend, the water surging over the spillway of the big Burdekin Falls Dam, 200km inland between Mackay and Airlie Beach, reached 4.4 metres above the dam.

That’s an estimated 1.5 billion litres of water rushing over the spillway every day - enough to fill a Sydney Harbour daily.

The dam draws on the big catchment of the Burdekin River, from tributaries both to the north and south to the main storage at Lake Dalrymple.

More rain is likely over the catchment as the monsoon trough travels south early this week.

As the rain continues to fall on the already flooded areas, the intensity is easing as the trough heads towards Mackay and Rockhampton, where falls of up to 200mm are expected.

"The whole system is moving farther south, so Ingham’s going into a period of less rainfall, a little bit of a reprieve," senior forecaster at the Bureau of Meteorology Brian Rolstone said on Sunday.

"On Monday, the bulk of rain will head down towards the Qld central coast around Rockhampton.

"We can expect local flooding to occur as that rain moves south."

But flood-affected residents in the north won’t have much of a reprieve as the bureau predicts the trough will return to the north."

A "vigorous" change will hit around Fraser Island on Wednesday and will merge with the monsoon trough at Mackay before making its way back up the coast.

"As time goes on, Thursday or Friday, Ingham will be back into it as it (the trough) moves back over the top of them with major rain.

"The hopeful thing would be that it keeps on going and heading further north, but we’re not too sure beyond Friday if it’s actually going to do that," Mr Rolstone said.

The western part of the state is also in for some heavy falls on Tuesday, forecasters say.

Torrential rain caused flash-flooding in Cairns on Saturday night, while the Herbert River near Ingham peaked at 12.25 metres for the second time this week, at 9pm (AEST) on Saturday.