Filamentous Green Algae

When you look closely at what initially appears to be green pond scum, it looks like it is made up of fine strands mixed with oxygen bubbles. These bubbles are released during photosynthesis or decay. Also called ‘pond scum’, ‘pond moss’, ‘water silk’ or ‘mermaid’s tresses’,  it is a filamentous green algae which, under favourable conditions, can form dense mats which resembles wet wool in static water or long, rope-like strands in flowing water. Its filaments consist of a series of cells being joined end to end giving a thread-like appearance. This form begins growing on the bottom or substrate and then lifts to the surface as buoyancy grows due to its production of oxygen. This form of algae may seem cottony, slimy, or coarse in texture.

There are many species which require a microscope to examine the cells to accurately identify. Here are 3 examples of genera:

Cladophora feels cottony and can form balls that float when the core decays. Magnification reveals long, slender cells and a branching habit.

Pithophora is sometimes called “horsehair algae” because of its coarse texture, which can feel like steel wool.

Spirogyra is bright green and slimy. Magnification reveals the chlorophyll-bearing pigments are shaped as spirals, the filaments do not branch.

It grows in running streams of cool freshwater, and secretes a coating of mucous that makes it feel slippery. It is also found in shallow ponds, ditches and amongst vegetation at the edges of large lakes.