We have a pond (not a koi pond) on our property. I recently bought a few water plants to enhance the beauty of the pond. I just noticed this evening that one of the plants has oval shape black spots on the leaves. I peeled them off the best I could without getting into the muck. I can't find out a name for these spots. If anyone has any idea, please let me know. they are not red and black or mis-shaped. They are egg shape and very black. Help??!!