Cooroy RAG 

 27 JUL 2007

BE warned - images of the Mary River choked with weed could indeed be a crystal ball glance at the future, should dual events occur. If river flows con­tinue to be compromised by a lack of rain events, or by the building of the flawed Traveston Crossing Dam, these “dead zones” could join to become a continuous strip of lifeless water cut­ting through neighbouring shires. Catchment officer Steve Burgess does not exaggerate when he says this is a major disaster just hanging in the balance.

“Of course weeds in the river is not a new problem, but we are looking at a system which has not received flush­ing flows for two years now.

“The levels of invasive floating weeds - water hyacinth and salvinia - are collecting in these big rafts and beneath them is no light~or oxygen, nothing can surface or dive through this mass.” The floating mats are the obvious sign of an impending prob­lem, but waiting in the wings is an even greater concern, with small colonies of the weeds tucked into banks in all the tributary creeks along the Mary River’s 300-kilometre length.

Mr Burgess predicts that a major flow event will flush these out Ito converge and create an even bigger problem for groups like the catchment committee. He estimates some seven kilometres of river near Gympie, including stretches at Widgee Crossing, are se­verely affected by the weed, which is floating in whole sections up to two kilometres long.

There has been on-going control of a similar problem at the river barrage near Tiaro, using mechanical harvest­ing and spraying, but Mr Burgess said an integrated approach along the whole river “from top to bottom” needed to be fast-tracked.

“There are people working towards this result, but what makes it difficult at the moment is the low flushing flows in the river,” he said.

“And that will be a major problem if the Traveston Crossing Dam goes ahead - this will become the usual state of the river, and this is what the sur­face of the dam could look like.”

The economic cost of such controls was also a burden, and the situation in the Mary is far worse than recently highlighted problems in the Brisbane River. Mr Burgess said authorities on the Hawkesbury River in New South Wales had just spent millions of dol­lars trying to control the problem, only to start all over again. He describes the situation as precarious and said it was too far gone for the existing intro­duced biological controls to have any effect. He said the best result would be to receive flushing rain which pushed the weed mat out to sea, but that in itself could be dangerous if the mass failed to break up along the way.