Little or no light areas produce a blue-green color. Algae also protect themselves by finding areas of a roof where moisture is most prevalent, as these areas are cool and shady. According to both the American Roof Manufacturers Association and the Canadian Asphalt Shingle Manufacturers Association, algae is only an aesthetic issue and not as much as a damaging issue for your roof.

However, roofs having algae on them attract other life forms that are capable of causing damage. Algae and fungus combinations create something called lichen, which is a photosynthetic fungus with roots that wrap around granules. The plant feeds on shingle filler, and once attached, lichen is hard to remove. Dried out lichen comes back to life when moisture or rain occurs, and oftentimes, power washing and scrubbing cause even more damage.