Mike, I guess I was thinking of the black, streaking type of algae growth. That's what we primarily get around here. I've never seen it cause wear. I've read this sort of explanation below several times. This is from the Certainteed site. "In certain moist areas, algae can grow on shingles. Although the algae has no proven effect on shingle life, it does stain or discolor the shingle. Commonly (and usually incorrectly) called fungus, this algae staining can be unattractive." .