Q: We recently had stones placed on the bank of our detention pond to prevent erosion. Many animals and birds live there. Weeds are growing between the stones. We need an environmentally safe herbicide to kill the unwanted plants.
A: I am comfortable recommending a glyphosate product that is labeled for aquatic use (click for sources) and which is then mixed with a non-ionic crop oil surfactant (Cygnet, Cide-Kick (click for sources) to help it stick to plant leaves. I have more details on pond weed control at Lake and Pond Weeds.
Weed killers that are considered organic and labeled for landscape use have not been tested for safety in pond environments so I do not recommend them.