Green groups say a new report shows turning north Queensland into a ‘mega farm’ would be costly and damage other industries and the environment.

Water from two rivers could be used to grow an extra 50,000 hectares of crops in north Queensland, a federal government report claims.

But an environmental group says the report shows the “mega farm” project isn’t viable as there isn’t enough suitable land and water in the area.

Deputy Prime Minister Warren Truss says the report, a result of a two-year study, outlines the opportunities for new irrigated agriculture in north Queensland.

He says Flinders and Gilbert river catchments could irrigate up to 50,000 hectares of land, potentially producing crops worth millions of dollars.

“While commitments would be premature at this early stage, the report gives us an excellent framework to focus on boosting agriculture in north Queensland,” he said in a statement.

He says the report also highlights a range of issues such as potential impacts on the prawn fishery industry in the Gulf of Carpentaria.

Wilderness Society Queensland spokeswoman Karen Touchie says the report shows the high cost and challenges of farming in northern Australia.

“The report is also clear that all the water currently in those river systems is being used,” she said in a statement.

She says diverting any amount of water for agriculture would impact the fishing and tourism industries as well as recreational users and the environment.

“Trashing [the rivers] simply to pursue a political agenda or perpetuate a discredited food bowl myth makes no environmental or economic sense,” she said.

Two potential dam sites were identified on the Gilbert River that would allow up to 30,000 hectares to be cropped – sufficient to sustain a sugar mill or cotton gin.

The report said damming Flinders River wasn’t commercially viable but off-stream water storage systems could be used to irrigate up to 20,000 hectares of crops.

Last year the Queensland government, which has promised to double food production in the state by 2040, announced it would open up Cape York to large-scale farming for the first time.