Question
I have a cement bird bath with running water but do develope a lot of moss etc. I reacently read that putting a water hyacinth in it could help keep it clear. However when I do research on the plant, there are many warnings about the damage it can do and how it multiplies. What do you think, or do you know who I could ask if you cannot help.
Thanks

Answer
I cannot imagine a birdbath large enough to accommodate a water hyacinth.  As to the damage it does or how much it multiplies, that depends on where you live.  Here in zone 5 there is no danger, as it cannot survive the winter.

You could just periodically scrub the birdbath with clorox and rinse well.  On the other hand, some people would consider the moss ornamental, and it does not harm the birds.