What’s wrong with willows?

?Willows have many serious and damaging effects on the waterways which they infest. These include the development of large fibrous root masses which spread into the watercourse, trapping sediment and affecting the flow of water. In some cases the flow is lessened to such an extent that the river or stream is reduced to stagnant pools of water. When a flood does occur, the water is diverted by these root masses and erosion occurs. Of course, these changes have many deleterious effects on native fish, animals and vegetation. These willows spread and colonise rapidly and in huge numbers so their control is urgent. For these reasons they have been listed in the top twenty worst weeds in Australia.