The most common culprit causing the black streaks on roofs is a blue-green algae called Gloeocapsa magma. Over the past 25 years this strain of algae has become more hardy and has migrated to less humid environments. It has now become a common sight on asphalt roofs across 80% of the United States. This Home & Garden how to video series shows how to clean your roof and get rid of the black streaks caused by algae. Learn how to inspect and use a cleaning system to get your roof looking brighter.