No, the weeds usually take the weedkiller in through their leaves. If the weeds are near a pond or you want to be more 'green', pour just-boiled water on the weeds. Any runoff won't hurt the fish/wildlife as it's just water. It smells a bit cabbagey though! Dandelions, however, will grow back again.

No just spray weedkiller straight onto weeds

I use Resolva, brilliant product and it does the job well, no weeding needed.