If you’ve looked up at your roof lately and noticed unsightly black streaks running down the shingles, you’re not alone. Many homeowners in Middletown, NJ and beyond wonder what’s causing the discoloration—and more importantly, whether it’s something to worry about. Spoiler alert: it is. Those dark stains are more than just a cosmetic issue.

Here’s what you need to know, straight from the experts at Power Wash Plus, your trusted local team for roof cleaning, soft washing, and home exterior care.

1. The Real Culprit: Gloeocapsa Magma Algae

Those black streaks on your roof? That’s a living organism—an airborne algae called Gloeocapsa magma.

It thrives in humid environments like ours here in Monmouth County
It feeds on the limestone filler in asphalt shingles
It’s most noticeable on the north side of your home, where the roof stays damp longer

People Also Ask: “Is roof algae dangerous?”
While not harmful to people, this algae damages your roof by holding moisture and promoting decay, shortening the life of your shingles.

2. Why Roof Algae Spreads So Quickly

Algae spores are airborne and can easily jump from one rooftop to the next—especially in neighborhoods with lots of trees and shade.

Moisture + shade = the perfect breeding ground
Limestone in shingles provides a steady food source
Lack of sunlight lets algae thrive undisturbed

If one house on the block has it, chances are yours will too—unless you take action.

3. Other Causes of Roof Discoloration

While algae is the most common cause of black roof streaks, other culprits include:

Mildew and mold – thrive in similar conditions and may co-exist with algae
Dirt and environmental pollutants – especially near busy roads or industrial areas
Tree sap or droppings – can stain shingles over time
Rust from metal fixtures – causes orange-brown streaks, especially around vents and chimneys

Each of these issues not only affects appearance but can also lead to roof deterioration if ignored.

4. Why You Shouldn’t Wait to Clean Your Roof

Letting roof algae stick around can result in more than an eyesore:

Shortens the life of your roof shingles
Retains moisture, promoting mold, rot, and eventual leaks
Reduces energy efficiency by darkening your roof and increasing heat absorption
Drops curb appeal and home value
May violate HOA rules if left untreated

Avoid the need for premature roof replacement—invest in professional cleaning now.

5. The Safe and Effective Way to Remove Roof Stains

High-pressure washing might seem like a quick fix, but it can actually strip away granules and destroy your shingles. That’s why we use soft washing—a low-pressure method with powerful cleaning solutions that:

Kill algae at the root
Gently lift and rinse away stains
Protect your shingles and extend roof life
Help prevent future growth with biodegradable treatments

Our team at Power Wash Plus is highly trained in this method, ensuring a damage-free, long-lasting clean every time.

Let’s Restore Your Roof—The Safe Way

Don’t let roof algae eat away at your investment. If you’re seeing black streaks or patches, it’s time to act. Power Wash Plus proudly serves Middletown and the surrounding area with professional roof cleaning that’s safe, effective, and affordable.

Call us at 732-671-6767
Request a Free Quote
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Let us bring your roof back to life—before those black streaks turn into a bigger, costlier problem.