I have an old pond. Every year it has dragonfly larvae and mosquitos, bloodworms and daphnia. This year my neighbour planted a poisonous passion flower climber which went into my garden. Since the leaves started rotting in the pond no life except plants and algae has been seen. How do I control the flower?

I didn't realize passion flower was so poisonous. I did a little internet research. It seems that the ornamental blue passion flower is the most poisonous, and others aren't as poisonous. People eat the fruit of some species. It's mostly the root that has toxins in some species and presumably the leaves. We've had a passion flower vine near our porch but not near the ponds.

How big is your old pond? I suggest pulling up the vine near the pond while wearing gloves. They prefer to grow upwards; do you have a trellis near the pond or something vertical?

Then, if the pond is small, a total cleaning should be done to remove all the leaves that went in in case they leached anything into the pond. Since you don't want to use any herbicides near the pond, pulling up any wandering passion flower every week or two is the best defense from future incursions. If the neighbor planted the vine close to your pond, perhaps you could convince him/her to transplant it to another location. If not, a physical barrier like a rock or fence wall between their land and yours might help.

There is a fence, but the flower climbs over it!

Anyway, there is no more green water problems and the pond is now home to 2 normal goldfish and 1 black backed goldfish (with an eye missing).

Big question I'd ask the neighbor would be 'do you prune or use trimmers to trim back the vine?'. My neighbors ( we're on good terms ) know that if their bushes start getting out of hand on my side of my chain link fence then I'll start trimming. It's not a case that I wanted to kill their plants, just control them on my side. It won't hurt to ask and explain that as an unfortunate accidental surprise it turned out to be poisnous and that all you need to do is trim it to the point it's not over the fence top.