Question: why do roof shingles get black streaks?
Answer: Answer. Those black streaks on your roof shingles are most likely an algae called gloeocapsa magma, or as it is more commonly referred to, a blue-green or black algae. Algae is a solid deposit of spores and dirt, another form of mold. ... Do NOT pressure wash your roof; one wrong angle and you can damage the shingles.