I certainly can't add to what Greenhead said, but I can tell you what I've learned so far on my pondmiester adventure.
First -identify the weed. If you don't know what you got, you won't know how to treat it. Do a google search on aquatic plant identification. Check this site out-http://www.tpwd.state.tx.us/fish/infish/vegetation/vegplan2001.htm
Second- Now that you know what the plant is you can find the best way to treat it- chemical, carp or manual labor.
I have 60% water milfoil coverage on my 8 acre pond. The fish population is very well balanced on all species. The LMB are only 80% of thier ideal wieght. They are not overpopulated and there is plenty of forage, but the forage hides too well in all the milfoil and the LMB can't get to them.I've worked at raking the milfoil out, it's like chipping away at the great wall of china with a dull spoon.It may work on your small pond.(bigger is not necessarily better with pond management!) This spring I will fertilize to create a bloom to reduce sunlight penetration, and add grass carp, even though some say they don't eat milfoil all that well. Other folks say they have had great success with carp vs. milfoil.(environmental variables) If I fertilize too late though I will just be feeding the plants. Its a tricky business.
Aquatic plants need 3 things- water, sunlight, and nutrients. Eliminate one of the big 3,(usually sunlight penetration) you're on your way. You can rake it all out, but it will grow back. As Bob Lusk says, It's like mowing your pond.
Good luck with it!
