What is filamentous algae and why is it dangerous to my pond?

What is filamentous algae and why is it dangerous to my pond?

Filamentous algae sounds nasty and looks nasty too. Filamentous algae is the type of moss you see on some ponds that has long, intertwined threads or filaments. The filaments can grow together to form a mat that seems like an icky, green wet wool or a mat of human hair.

Most people would recognize filamentous algae better by the simpler terms “pond moss” or “pond scum”.

Filamentous algae in threads.


It starts out growing on the bottom of your pond in shallow water or attached to structures in the water like docks, rocks or plants.

Pond moss offers no real value to recreational ponds, and instead can be very hazardous, toxic and a yucky, ugly nuisance to swimmers and sport fishing. It cannot be directly used/eaten by aquatic animals. The best thing we can say about it is that in some non-recreational lakes, the algae can be somewhat beneficial but only when it’s kept at a low level. Pond moss can make for decent cover for aquatic animals such as snails, some insects and scuds. (Scuds, aside from being popularized in the 1st gulf war as short-range missiles, are also a tiny form of crustacean that look similar to shrimp.)

A scud. Ain't he a pretty little guy?

A scud. Isn’t he a pretty little guy?

Typically however, filamentous algae can be a huge detriment to the life of a pond. It reproduces at an amazing rate; you might not see any and then all of a sudden have a huge algae bloom. As the algae grows and grows it gives off oxygen. The oxygen gets trapped in the weave of intertwined threads of algae and whole bunches of it rise to the surface.

Algae has a short “shelf life” however, and as it dies off it is consumed by decomposer bacteria. This bacteria gives off dangerous CO2 (carbon dioxide). If there’s enough dead algae and enough bacteria, the CO2 levels could be dangerous. Low oxygen levels can lead to fish kills.

The pond can quite literally choke itself out and become a dead zone.

So it’s a good idea to keep an eye on just how much algae is in your pond. There are ways of controlling or completely getting rid of filamentous algae which we talk about in other articles.

If you’d like more information, don’t hesitate to contact us with questions!

Call us (1-877-772-MUCK) or email us!

How to get rid of moss in farm ponds

How to get rid of moss in farm ponds

Filamentous algae, commonly called “moss”, or “pond moss”, is prevalent in many organically rich pond environments.

This moss covers the surface of the water and is aesthetically displeasing.  Chemicals can kill algae, but the breakdown of the dead plants just adds more nutrients for the next generation of algae.

Because farm ponds typically contain runoff water from phosphorus and other chemicals, algae can be more prevalent and problematic there. Phosphorus is commonly used as fertilizer for farming. Unfortunately the downside is that it can go into nearby water sources and help to create algae blooms.

Filamentous algae

Filamentous algae pulled right out of a farm pond

Phosphorus is a weird chemical too… unlike other fertilizers such as nitrogen, phosphorus doesn’t soak into the ground as easily. Instead, phosphorus moves downhill across fields. This is why it has been such a big problem in some larger lakes, creating toxic algae blooms in areas such as Toledo, Ohio and Grand Lake St. Marys, Ohio.

The physical removal of the floating algae is very time consuming and is short lasting.  The algae soon reappear in just a few short days.

To control moss you must control or manipulate its resources.

Algae need 3 resources to thrive.  Take away or manipulate their nutrients (sediment removal), environment (aeration), and sunlight (pond dye) and you can control this pesky plant.

If you need some help with your pond, contact us today! We’d love to help.

Call us (1-877-772-MUCK) or email us!