If you have noticed discoloration or any type of dark streaks along with your roof shingles, it is likely you are experiencing some type of algae growth. These growths can be extremely common in humid areas like Florida. Top 3 discoloration causes: Roofing Shingle Algae – Algae feed on the limestone that is used in the fillers around the asphalt shingles. Unfortunately, algae can infest your roof, trapping moisture and eventually causing water damage. Additionally, algae discolor the roof affecting the aesthetics and overall curb appeal of your home. If left unchecked, algae will eventually combine with fungi to form a lichen. And unlike algae, lichen is very difficult to get rid of. Asphalt Bleed-Through – These extreme environmental elements can cause the shingles to deteriorate immensely over time. Consequently, this deterioration causes the pigments of black asphalt in each shingle to rise to the surface in a process called asphalt bleed-through. These pigments can then bleed off the roof in a runoff after heavy rain or snowfall, forming black streaks of asphalt particles. This process can also occur with relatively new roofing materials if the shingles are of lower quality. Rust Stains – Metal roofs or roofs with metal fixtures are highly likely to see dark red or brown discoloration. This is an indication that your roof has rust stains.  If your roof uses metal materials, the red stains will be more widespread and become more obvious with time. However, if you have a roof with metal elements such as a metal chimney, metal flashing, antenna mounts, or any other metal components, the rusting discoloration will appear just around the metal components.