Concern is building over the proposed Gin Gin re-regulating weir, with Dr Martin Mallen-Cooper, an internationally recognised expert in fish ecology, expressing that he has some major concerns for the future of the Macquarie River if the structure is built.
"The proposed Macquarie Re-regulating structure would have a major negative impact on the river ecosystem, reducing biodiversity and reducing native fish populations," Dr Mallen-Cooper stated.
The fish expert said that he has four major concerns around the structure, including the interruption of tributary flows.
"All environmental water is not equal. River flows that are uninterrupted by dams and weirs have extremely high ecological value, compared to flows that are stored in dams and weirs and re-released," he said.
"Uninterrupted river flows pick up nutrients, especially carbon such as dead eucalyptus leaves, and generate natural productivity of plankton, which is the essential food source of fish larvae. This is the fundamental process of river ecosystems that sustains native fish populations.
"If flow is uninterrupted over long distances, it has even greater ecological value as this enables fish that are a long distance downstream to detect the increasing flow (fish can sense the slightest increase in water velocity and have an extremely acute sense of smell) and migrate upstream to spawn so their larvae have greater survival."
The internationally recognized doctor also stated that he has major worries around the impacts of variable water levels on river-edge and channel habitats.
"Tributary rivers of the northern Murray-Darling Basin have highly variable river levels, from floods to droughts. However, these water levels vary over a very consistent regime over time - rising in floods but spending a lot of time at a low level with varying baseflows. The time-scale and season of this variation is very important for fish," he added.
Also on Mallen-Cooper's list of concerns was the impacts on flowing-water habitats.
"Rivers have a natural mix of flowing and still water habitats," he said.
"Standing beside a healthy river, we all visually recognise flowing water and we recognise eddies, backwaters, pools and riffles - that is, healthy rivers have diverse river hydraulics. This hydraulic diversity provides habitat diversity and biodiversity."
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