This may not be the correct forum to ask about this, but I figure a lot of
people have concrete bird baths in their gardens. One of my bird baths, it
is concrete, grows some sort of red crud that discolors the water. It
actually cakes on the surface when there is water in it and can be chipped
off when it dries. My other concrete bird bath doesn't do this. Any idea
what it is and what's causing it? Is it harmful to birds? Any way to get rid
of it?

Thanks in advance.
Karen
Portland, OR