Water Hyacinth

According to the CSIRO the water hyacinth (Eichhornia crassipes) native of the upper Amazon, is one of the worlds' worst aquatic weeds, forming a dense mat that can double in size in a few weeks, totally clogging waterways.

It was first noticed in Australia about 1890, probably brought in as an aquarium plant and has now spread to all states.
In the 1970's and again in 1980's biological controls were introduced with the release of a variety of weevil and a moth which has worked well in sub tropical areas of the eastern states, and another weevil species was released in the 1990's.

The plant shown here is growing in my frog pond, I have to thin it several times during the summer growing season, the roots form a big thick fibrous clump under the water.
It is probably something I shouldn't grow, but then that could be said of most of our introduced garden plants.
I make sure the discarded plants go into the compost bin, and cut the flower heads after flowering. As we are not close to a waterway and have no run off I grow it simply because I like the flowers.