Blue-Green Algae (cyanobacteria)

Definition

Although most common in their green or blue-green form, blue-green algae can also be reddish-brown. The algae are composed of cells that house cyanobacterial toxins. They flourish in ponds and lakes during the summer months, as they like still water during the hot season. The algae may discolor the water, form a "scum" on the surface or create a foul odor.

Effect on Aquatic Life

Between 30 to 50 percent of cyanobacteria is non-toxic. Although the toxic forms typically do not harm fish directly, large quantities of the algae can use up the oxygen in the water, suffocating the fish. However, people who wade in the water or handle the algae can get skin irritation or respiratory infection. There are no reports of people in North Carolina becoming sick from blue-green algae.

Causes of Blue-Green Algae

In addition to high outside temperatures and still water, cyanobacteria seem to like water that is high in nutrients, especially phosphates. In water that has been overloaded with phosphates because of detergent or fertilizer, the algae are particularly plentiful. Thus, they seem to flourish in water that has been polluted or is subject to nutrient loading because of man-made materials.

Source: Health Canada