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Water Weeds
27 Sep 2013
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Over the three years from when the Barrage was completed, weeds from outlying areas thrived in the new freshwater environment.  Probably the most serious infestation was that of Water Hyacinth.
Water Hyacinth, which is native to the Amazon Basin, was first brought to Sydney, Australia as an ornamental plant in the early 1890's.  Within ten years, it had spread to infest river systems and water courses up the Queensland coast, including the Fitzroy.
In 1973, the river's surface was so infested in hyacinth for 50km above that barrage, that a small animal like a dog, could easily walk from one side of the river to another.  In this photo, you can see how much had even gone over the barrage gates and floated down in the city reaches of the river.
In January 1974, after some years of drought, the Fitzroy hinterland had flooding rains and the barrage gates were opened, allowing the river to flush itself of the pest.
Through constant vigilance using chemical sprays and the introduction of four South American weevils that eat hyacinth, the weed in now under control.  
The lastest threat is the grass, hymenachne.  In recent floods, large islands of this weed detached from the riverbank, have been seen floating down the river and out to sea. Hymenachne is an invasive weed with the potential to have major environmental impacts in many parts of northern Australia. Introduced as a fodder crop for cattle in the 1980s, this grass has now invaded wetlands, waterways, irrigation and drainage systems, and low-lying commercial enterprises such as sugarcane farms.
Hymenachne poses numerous economic and environmental threats to primary production, water resources, fisheries, conservation and tourism.
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