I am wanting to spray some pre-emergent on the backside of some of my pond dams to prevent much of the fast growing brush like vegatation that comes up. I have a good stand of grass but all the other plants seem hard to control. I am concerned though about anything that might negatively effect my fish. Runoff fro the backside of many of my dam locations flows into other ponds I have. Any suggestions of a safe chemical to spray? Or should I just forget it? I don't want to do anything that is not healthy for the overall ecosystem.