Why do I need to know what type of water weeds I have? Isn’t it better to know your enemy so you can attack its weakness? Knowing the type of weed will give you an advantage when deciding the course of action to take. Weeds are all different, they can propagate by seeds, fragmentation, and by nodes. Changes in temperature and PH of the water can effect some weeds. Time of the year is another parameter that needs to be discussed.