Water hyacinth
Water hyacinth is a very attractive water plant but one of the world's most serious weeds. In tropical regions in Asia, Africa and America it constantly threatens to choke water ways making them inaccessible to commerce. Rafts of the weed seriously interfere with irrigation and fishing. It is a serious problem in the coastal rivers of Queensland and northern New South Wales. It has also proved that it can adapt to temperate inland lagoons and rivers in New South Wales, Western Australia and along the River Murray in South Australia.
The NSW Department records provide a description and images of water hyacinth.
Water hyacinth is one of the world’s worst aquatic weeds. It infests rivers, dams, lakes and irrigation channels on every continent except Antarctica. It devastates aquatic environments and costs billions of dollars every year in control costs and economic losses.
Water hyacinth is native to the Amazon basin in South America and was brought to Australia in the 1890s as an ornamental plant. The first record of water hyacinth in New South Wales (NSW) was in 1895. In 1897, the government botanist Mr J.H. Maiden noted that it had spread rapidly in the ponds in the Royal Botanic Gardens in Sydney. At that time, he warned that the plant should be kept away from the northern rivers where it ‘may very rapidly become a serious pest’. Unfortunately, this warning went unheeded and by the early 1900s it had spread along the east coast of Queensland and the north-eastern regions of NSW.
Water hyacinth is justifiably called the world’s worst aquatic weed due to its ability to rapidly cover whole waterways.
In Australia, it forms dense, impenetrable mats over the water surface. Specific impacts include:
- blocking irrigation channels and rivers
- restricting livestock access to water
- destroying natural wetlands
- eliminating native aquatic plants
- reducing infiltration of sunlight
- changing the temperature, pH and oxygen levels of water
- reducing gas exchange at the water surface
- increasing water loss through transpiration (greater than evaporation from an open water body)
- altering the habitats of aquatic organisms
- restricting recreational use of waterways
- reducing aesthetic values of waterways
- reducing water quality from decomposing plants
- destroying fences, roads and other infrastructure when large floating rafts become mobile during flood events
- destroying pastures and crops when large floating rafts settle over paddocks after flood events.
Water hyacinth will rapidly take over an entire waterway. Under favourable conditions it can double its mass every 5 days, forming new plants on the ends of stolons. It also grows from seed which can remain viable for 20 years or longer. This enormous reproductive capacity causes annual re-infestation from seed and rapid coverage of previously treated areas, making ongoing control necessary.
Water hyacinth in South Australia
The first serious infestation in South Australia was found covering the Ramco Lagoon on the edge of the Murray near Waikerie in October 1937. Plants had been thrown into the Lagoon from a nearby garden fish pond. This initiated an eradication program relying on hand removal from boats. (Herbicides and biological control were then not available)
The South Australian Government appealed for financial help from the Commonwealth and the River Murray Commission. They refused, so grants were made available by the South Australian Government to the local government councils involved.
While the New South Wales and Victorian authorities searched the Murray and its tributaries within their boundaries, the councils and the Agricultural Bureau began a well advertised campaign in South Australia.
Coloured warning posters were widely distributed throughout the Murray-Darling Basin at a cost of £180. Special booms were set at strategic places across the River to catch the floating weeds.
A report dated,15.8.41, from the Chief Engineer of the Engineering and Water Supply Department stated that water hyacinth had been eradicated down to Mannum, the furthest found infestation.
That was not the end of the problem. In April 1955 plants were found in Zeiglers Lagoon near the original Ramco site. In December 1961 specimens were found for sale in a number of plant nurseries in the metropolitan area of Adelaide. Warnings in the media revealed plants in private fish ponds which in some cases were loudly defended by the residents arguing that they could not possibly infest the water ways.
A much more serious problem was revealed when large infestations were found, in the early 1980s, in the Gingham water course near Moree. This water feeds into the Darling River system and therefore presented a potential threat to the inland rivers including the Murray in South Australia. South Australian Weed control officers assisted with the eradication program for many months.
History tells us that water hyacinth requires continued vigilance.