If you reside in a humid part of the country, you probably would have seen some unattractive dark streaks on asphalt shingle roofs. These black streaks are attributed to a build-up of dirt, and faulty shingles, but these are not the main culprit.

What Are Those Black Streaks on Your Asphalt Shingle Roof?

Although these black streaks appear like dirt, mold, or soot, what they are is an alga called Gloeocapsa magma (commonly known as blue-green algae or black algae).

Gloeocapsa magma usually appears as small spots in its early stage. At maturity, it becomes a visible streak. At this stage, before the homeowner notices the algae, it would have stayed on the roof for at least 2 to more months.

This alga creates a protective dark pigmented outer coating that protects it from destructive ultra-violet rays hence the black appearance.

Why is this alga most common in asphalt shingle roofs?

Gloeocapsa magma spores are airborne. They can spread by wind, human clothing, and animals. Because of this, they can spread from roofs to roofs in a neighborhood. 

To reduce cost, most asphalt shingle manufacturers make shingles containing asphalt but majorly made of fillers (fiberglass and crushed limestone). These fillers are the algae’s food source, thereby attracting them and encouraging their growth.

Is Gloeocapsa Magma harmful?

Gloeocapsa magma is not dangerous in itself. But as time goes on, it can lead to the protective ultra-violent granules that protect the shingle coming off, and finally, drying them out.

Gloeocapsa magma can also combine with a fungus (airborne) to form a symbiotic relationship called lichen. The algae provide for the lichen. But unlike algae, the lichen can grow roots, making it harder to eliminate than only algae.

How do you remove black streaks on your asphalt shingle roof?

Gloeocapsa magma can easily be removed simply by cleaning the roof. Contact a professional roof cleaning company to get the job done right the first time.

How to prevent black streaks from your asphalt shingle roof?

Can you permanently eliminate Gloeocapsa magma? No. This algae, just like every other airborne microorganism, can only be prevented, not eliminated. How?

Maintain your roof; you should always clear off accumulating debris from your roof. It deprives the algae of having a conducive environment for growth. Also, keep your gutters clog-free to ease water drainage. Clogged drainage is a suitable environment for algae growth.


Gloeocapsa magma can be unattractive, but it is easy to eliminate it, and there are various ways you can prevent those black roofs from reappearing. The easiest way is to hire a professional roof cleaning company for all your roof cleaning needs!

Reach out to us at (Brilliant Exterior Services) for a free quote today! (336-355-1943)