Blue-green algae

Blue-green algae

Algal blooms come in two forms, but blue-green algae (cyanobacteria) blooms are almost always planktonic. Therefore, if a bloom has filaments, it is most likely an algae bloom. Filaments are never found on blue-green algae blooms that produce toxins. Bodies of water with high levels of blue-green algae often resemble split-pea soup. When blue-green algae blooms are very large, they tend to form solid-looking clumps. A slight swishing with the hand will break up the clump, and the bloom will still easily pass through the open fingers of a cupped hand.

Some types of algae produce planktonic blooms, such as diatoms, which usually grow in springtime and colour the water brown. At the beginning of spring, a thin layer of brown mud can often be found on rock surfaces in watercourses and is normally due to diatom colonies. Euglenoids (flagellate protozoa) leave a powdery film on the surface of the water; some give the water a bright green tinge, similar to antifreeze. Under a strong light, euglenoid blooms change from green to bright red due to a pigmentary reaction when exposed to ultraviolet light stimulation.

Blue-green algae often clump together, particularly under calm conditions.

Occasionally duckweeds are mistaken for algae. Duckweeds are actually small, floating plants, and can sometimes grow to cover entire water surfaces. They are identified by the tiny white root that hangs from their lower surface into the water column. Duckweeds do not produce the pea-soup blooms characteristic of blue-green algae, or produce toxins. Duckweeds are beneficial plants that remove phosphorus from the water, and can dominate over blue-green algae and algae if conditions are suitable.

Duckweeds are not algae or blue-green algae.