Mine don't appear to be water marks; I was just wondering if it might be scarring from bits of sand that are blown against the falls. I will need to be more attentive and see if the irises that are not exposed to the wind (we are in a windy area) get the same little white specks where they're not supposed to be.
Sometimes I get white strings on them that I am pretty sure are spider webs that have gotten blown against them. I haven't figured out how to get them off, but at least they don't cause any damage.
