Spreading across the country since the 1970s, this yellow and green stemmed plant can re-grow from the tiniest fragments. It lives in a variety of habitats, from three-metre-deep waterways to damp ground out of water. It's quite common around the edges of some of our reservoirs.
The weed has the potential to cause absolute havoc along our canals and rivers. It forms a dense mat over the water's surface that blocks out light and oxygen, killing anything living beneath it and blocking navigation.
It is practically impossible to eradicate, with some suggesting the best way to control it is to fill in the ponds where it is found and dig new ones.