Filamentous Algae Explained

Filamentous algae—also known as string algae or pond scum—are a persistent nuisance in backyard and farm ponds. These long, hair-like strands form thick mats on the surface, interfere with aquatic life, and make your water look and smell unpleasant.

In this updated guide, we cover:

• What filamentous algae are

• Why they thrive

• Natural and chemical control methods

• A proven product that eliminates them effectively

What Is Filamentous Algae?

Filamentous algae grow in long, stringy strands that tangle together into mats. You may find them:

• Floating on the pond surface

• Attached to rocks, plants, or liners

Common names include:

• String Algae

• Blanket Weed

• Pond Scum

Why Filamentous Algae Are a Problem

These algae:

• Reduce oxygen in the water (especially overnight)

• Compete with beneficial plants

• Cause unpleasant smells and aesthetics

• Can be harmful to fish if untreated

How to Get Rid of Filamentous Algae

1. Manual Removal
Use a rake or pond skimmer to remove algae mats. This is a temporary fix but helps reduce nutrient load.

2. Copper Algaecide – Try Captain®
For quick and effective results, Captain® is a top choice for filamentous algae control.

Why Choose Captain?

• Double-chelated copper formula (9%)

• Works within 3–7 days

• No waiting period for swimming, fishing, or livestock use

• Safe when used as directed

Buy Captain Algaecide Now

4. Add Aeration to Improve Water Quality
Increasing water circulation is one of the most effective ways to prevent filamentous algae from taking hold. Aeration improves oxygen levels, supports beneficial bacteria, and keeps your pond balanced.

Healthy Ponds offers a line of high-efficiency aerators designed for ponds of all sizes. These units:

• Help break up surface algae mats

• Reduce stagnant zones where algae thrive

• Support a healthier, oxygen-rich environment for fish and plants

5. Prevent Future Algae

• Limit fertilizer near the pond

• Add shoreline plants as a buffer

• Avoid overfeeding fish

Not sure what your pond exactly needs? Reach out to our pond experts. We have many years of experience treating ponds healthyponds.com/free-pond-plan