Chemicals can be effective, though there are many variables to consider, including your own feelings about using the same. I have used a product called Sonar and it works quite well. (Affects the pigment producing function of the plants. They turn "white" and dye from interruption of photosynthesis)
It is generally "safe" for people and wildlife, but really expensive. Amount needed depends upon the size of the pond and flow in and out, if any. One thing to remember if you have a fish population you want to maintain is that even if the chemical is harmless to them, large quantities of dying plants will sap the oxygen level substantially. That alone could result in die off. You should be able to do a search on aquatic herbicides and find other alternatives to Sonar along with safety information. Good luck.