Water hyacinth
Hyacinth can block entire river systems, shading
out the river and starving the water of oxygen
Photo: Greg Calvert
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In north Queensland, three floating plants are declared weeds.
Water hyacinth, whose pretty blue flowers inspired its introduction
into fish ponds and aquariums, quickly found its way into local
waterways and spread rapidly. It can block entire river systems,
shading out the river and starving the water of oxygen. All the
native water plants die in the deep shade and fish can suffocate.
Although some people use it for mulch, such harvesting does not
appear to make much of a dent. Due to active transpiration of water
through the leaves, water hyacinth acts like floating water pumps
and contributes greatly to evaporation of water from dams.
Salvinia molesta
The hyacinth shares north Queensland's local waterways with
another weed: Salvinia molesta, so named because it molests
and destroys water ways.
Salvinia: the molester and destroyer of water
ways
Photo: Greg Calvert
|
Salvinia is actually a floating fern and, like hyacinth, tends
to reproduce vegetatively rather than sexually. It grows extremely
fast, doubling in size in just three days.
Once, it formed great mats across Ross River in Townsville, so
thickly that people were able to use the weed to walk across the
river. Nothing can live beneath such a smothering surface.
Fortunately, this weed too has been reined in by the introduction
of a particular weevil and it now exists in only small pockets.
Water lettuce
A third invasive water weed is the water lettuce, Pistia
stratiotes. For some reason, it has not been so prolific in
Queensland. Some say it is due to competition from hyacinth,
however, the reduction in hyacinth has not seen an explosion in
water lettuce.
