Are Hollyhocks Toxic to Ponds and Their Fish
My pond is turning mucky and green. I know the green is algae but I have noticed a plant the is growing just on the outside of the pond and it does touch the water. I believe it is the reason for the pond's muckiness and the horrid smell.
Certified GKH Gardening Expert
This article may help too: https://www.gardeningknowhow.com/ornamental/water-plants/wgen/algae-removal.htm
I find no data showing Alcea being toxic to fish. As far as the muck and smell of your pond, this article might be of help: https://apps.rhs.org.uk/advice/profile?pid=447