How to safely kill and rid a pond of lily pads, string algae?

Thanks. The pond is surrounded by trees. Lily pads so invasive you literally could not see any water, just a thick rug of lily pads. They are not easy to pull up, the roots are as big around as my arm and are interconnected like the interstate system on the map of the USA. I spent years puling them up, root and all. Never could get all of them. Then spent several years spraying to kill (stuff that does not endanger fish and such) But they come back. A few would not be bad, but that is not what happens. I'll try a dye this year also to provide shade, hoping that helps. The string algae is a problem and the algae that is prolific that I thought was just some kind of grass (red grass) but through research found out it was also algae. I pulled a huge amount up last fall, but I bet it will be bad again this year. It will be impossible to completely pull it all up, just way too much of it.

not sure the name of them, yes they bloom, white or yellow flowers