SUGARCANE farmers have been blamed for being the "major culprits" of farm pollution that has ended up on the reef.
"They are using frankly far too much fertiliser than what is required to grow the crops," WWF reef campaigner Louise Matthiesson said.
At a Great Barrier Reef lecture in Brisbane, she said excess fertiliser washed into rivers that flowed onto the reef.
"When you pump that much fertiliser onto the reef you get a hell of a lot of water pollution, it feeds the growth of crown of thorns outbreaks and algae that smothers coral."
The day before Ms Matthiesson addressed a room full of people at Queensland University of Technology, a scathing report was tabled in Queensland Parliament about the state's plan to tackle poor water quality in reef catchments.
In the water quality report, the Auditor-General found land management practice programs were not achieving the changes needed.
It also said recent relaxation of land clearing rules increased the risk of sediment runoff, working against the reef plan's goals.
"What the Auditor-General is saying is that it's not going to work if we just keep doing things the way we have been," Ms Matthiesson said.
"We need a radically different approach."
She said regulations and a pollution cap should be put in place.