Filamentous algae, as the name implies is structured with string
like, or filament like growth. This is why another common name for this
family of algae is "string algae".
This algae may vary in color, mass, and density, and most often it will appear like spinach or fuzzy hair like masses.
Filamentous algae can grow in ponds of any size and can often
overtake ponds with high organic nutrient loads. These nutrients may
come from things such as fish waste, fertilized run off, or decaying
organic materials in the pond itself.
Limiting all of these things will often help control string algae a bit better because they are at the root of why algae may or may not grow in a pond.