Filamentous Algae


Filamentous Algae will often form mats that float on the surface of the pond resembling wet wool. Most pond owners commonly refer to this type of algae as "pond scum", but can often be called string algae, or floating algae. This is a very common type of pond algae, but if left untreated can cover the entire surface of your pond.

Mechanical Control

Filamentous Algae can be removed from the pond by raking. Using Pond Dye will help to limit sunlight into the pond for algae to complete photosynthesis.

Reducing the overall nutrient load in your pond will help to keep algae blooms to a minimum. Use PondClear or MuckAway to reduce overall nutrients.

Chemical Control

There are several chemical pond treatments for algae. They should be applied when the algae is actively growing. Applications should begin when algae first appears as long as your water temperatures are above 60°F. Over time, the algae will begin to brown and die. Once it is completely dead, use a rake to remove dead algae away to prevent an accumulation of dead algae and muck. Unless steps are taken to reduce the overall nutrient load, multiple applications may be needed for full season control.

Selecting the Right Product

Not sure what treatment is right for your pond? Click here to view our product selection guide or choose from some of our most popular products.

Popular Chemicals:

Chemical Application Best Practices

Anytime you use chemicals treat weeds and algae, please keep in mind the following:

  • Treat your pond in sections. Treat only half the pond's surface at a time. During hot weather or when treating heavy growth, it is important to treat no more than 1/4 of your pond at a time and wait the full 14 days before re-applying. This helps lower the risk of fish loss during hot weather or when treating heavy growth.
  • Once the weeds have browned & died, use a weed cutter & rake to remove as much dead material as possible. This prevents an accumulation of dead plant material and muck.
  • Take a proactive approach to pond management. Use PondClear, MuckAway and Pond Dye to keep your pond looking great. For more information, see our article on the Airmax  Ecosystem .

Ask an Expert

If you are unable to identify your pond weed(s) using our Weed ID Guide, follow this article to email us a photo.