Shorty:
Take it from someone who has "been there, done that" you are a lot more likely to lose the pond (as you put it) by the wrong or too much chemical than you are by letting nature, and cold weather run it's course.
Do your research carefully and make as accurate an estimation of your lake size and what weed you are faced with as you can and you will be doing the right thing.
I believe one of the biggest mistakes a Pond Boss can make is to look for a cheap way of doing it.
Each of us has likely spent thousands, tens of thousands, or hundreds of thousands of $$$ on their land, lake, etc. Saving a few bucks by using chemicals that are potentially harmful is not the best approach.
Bing
