Haven't seen that before on waterlilies. If you can't see anything on the upper surface that might be causing it try looking on the underside of the leaves.

Thanks tropicbreezent. I'll check under the leaves. Would it have anything to do with the fertilizer tabs I've been very generous with? I really haven't seen much going on around that stock tank., insect-wise. It almost seems like it must be a virus or something, rather than an insect. (But then again, maybe I'm just fixated on "virus" these days!)

Hmmm......I checked under the leaves and they all had these red marks on them. Then I realized, that was normal for this variety. haha I saw no sign of bugs on the underside of the leaves. But....The ones that are affected are all around the edge. And I could see lots of small particles of the Mosquito dunk around the edge of the stock tank too. Could the mosquito dunk be causing this? None of the inner leaves have those yellows spots. Strange. I don't

know how or what from the mosquito dunk that could have done this........but it's the only thing I could make a connection with.

It reminds me of the damage done when insects like aphids inject infectious pathogens into plants while they're sucking out juices. Although, I've had aphids on Lotus (high above the water) but never on lily pads. Maybe there are other insects that do the same, just a thought. Can't imagine it being fertiliser, unless some got sprinkled on them. Don't know what mosquito dunks are made of, haven't used them.