that forum also mentioned that euphorbia is toxic to livestock, I suppose that could mean, being cautious, any animal that might eat it. Pets, neighbors goats or horses ect. I believe lantana and larkspur are also toxic to livestock and readily reseed under the right conditions.
There is a pastsure not far from us that is full of lantana and cows. We dig it out of our pasture cause its not supposed to be good for them. I do have it in my garden out front but it is a hybrid and doesn't seem to spread as I've had it for a long time. The butterflies love it. But not the birds.
I do know from experience water celery and elephant ear don't kill fish. My koi ate all the water celery I put in their pond the first day. They don't eat the umbrella plant but it gets so tall I'm always in pond clipping it off to start again.
Happy ponding all.