Big, Green and Rough: Cladaphora Algae Blooms in Austin Creeks

OMG!! What has happened to my creek? It’s chock full of some sort of horrible, green slime monster!

A man holding Cladophora.

A close up of Cladophora.  Image by Martha Cook.


That’s the filamentous algae we call Cladophora (above right), a nuisance species that often blooms very intensely in Austin area streams in the spring and sometimes fall. It is a branched, attached alga that has a rough, “wooly” feel to it, not slimy at all.

A thick blanket of Cladophora on top of the water.

A stream with several patches of Cladophora on the surface.


Cladophora loves fast flowing water, lots of nutrients and lots of light, so when these three things come together, it can be overwhelming.

Don't over-fertilize.  Visit for more informationIt forms thick mats that can take over the entire water column of a stream, especially in the late winter or early spring when maximum sunlight reaches the water, and nutrients are readily available.

Despite the unflattering images of “creek scum”, algae play a vital role in our creeks by providing oxygen, food, and habitat for aquatic organisms. However, when algae grow in excess, they consume oxygen in the water during the process of decomposition which can cause fish kills.

So remember, it’s just a symptom, not the source of the problem, which is usually high nutrients washing into the stream from stormwater! Nutrients may come from natural sources like breaking down of leaves but also human sources like fertilizer runoff and wastewater leaks. Visit to learn how you can keep the green in your yard, not in our creeks.

The Big Three. Three posters being held by three men: Don't over-fertilize. Accept a few weeds. Just kill the bad guys.