re: aquatic weed killer

this year has been horrible with the banks around our pond, we skipped some weed eating and it seems like it grew so quick and very thick, out of control.
We got it all cut down but we want to spray something to help kill roots and not come back. What is growing out into the pond we have had to rake out in the past. Was hoping there may be something to kill it. Didn't think about only spraying part of the pond at a time. Great advice!