From what I understand, if you make the water deeper (scoop out some of the dirt) they will not grow. Apparently, they do not grow in deeper water. Otherwise, the vinegar herbicide recipe might work. I don't think it will harm the fish & other wildlife near as much as would Rodeo.
Check this out: "...The U.S. Department of Agriculture does not endorse Rodeo..." taken from the following web page: http://www.npwrc.usgs.gov/resource/plan ... l/linz.htm
Now don't trust all the information on this page. Just as Monsanto claims Round-Up is safe, does not make it so. By the way, Monsanto makes Rodeo as well.
Rodeo is like Round-Up in that it contains the active ingredient glyphosate.