Irrigation Canals and Drainage Ditches.. Canals bring surface water to farmland, while ditches carry rainwater and water from the fields to the rivers. When weeds infest these areas, water can slow to a standstill and increase the risk of flooding. Aquatic weeds also cause clogging of irrigation pumps serving farmland.
 

	Giant Reed along a canal
	Himalayan Blackberry along a drainage ditch
	Parrots Feather