I need to eradicate some water celery that was introduced along one edge of my koi pond. I had it in a pot one summer, but it escaped when I wasn't looking, and now I have a mess. It is on the shore in the soil and rooted in the gravel in the pond along one edge. It is intertwined with all of the rocks, and is slowly taking over. It has to go! For those not familiar with this plant...it spreads by runners and roots anywhere it can. Hence, pulling it is out of the question...you can NEVER get it all, and it will sprout from a root fragment left in the water or on moist soil. I dislike using chemicals, ESPECIALLY around my pond, but I'm open to anything that will kill it. I've considered covering it with plastic to bake it, but that would not kill what's in the water. Same with a weed-killing torch. Short of disassembling that whole corner of the pond, I don't know what to do. Is there a weed killer that won't harm my fish/toads/frogs, OR my water lilies (which are rooted in the gravel...I can't move them to safety)?? Thanks.