Do you mean buttercup? I am not familiar with a plant called butterbur so perhaps you can send me a photo. Controlling weeds near a creek is tricky as you do not want any herbicides getting into the creek water. Some creeks are also used for salmon spawning and so changing the bank or water depth by removing native plants can also be harmful. If butterbur is an invasive weed then removing it may actually increase the water quality in the creek. If possible, it may be best to hand pull it from the banks. Keep growing, Marianne Binetti