Algae Awareness

Algae, a diverse group of mostly aquatic plants, can be found in both salt water and fresh water. The freshwater forms tend to be small, the vast majority being microscopic, although they often betray their presence by discolouring water. Most algae are harmless to humans and animals but a few are highly toxic, particularly some of the blue-greens which actually resemble bacteria more closely than the true algae.

For convenience, all the freshwater algae can be grouped into four main categories:

• Flagellates can swim independently and in large numbers can often affect the taste and odour of drinking waters.
• Diatoms are usually brown or yellow in colour and are mostly free floating, while some types often attach to the stems and leaves of other water plants, coating them with a brown slime.
• Green algae, which come in all shapes and sizes, are commonly present in reservoirs and dams, rivers and channels, on the sides of tanks and drinking troughs and in thick, tangled masses in low-lying swampy areas. They are not usually toxic but can clog filters, meters, valves and trickle irrigation lines.
• Blue-green (cyanobacteria) algae can range in colour from yellow to purple. Some types can be highly toxic to humans, livestock and birds. They are capable of very sudden, explosive growth and may appear as a thick, smelly, green, paint-like scum on the surface of a lake or dam, particularly around the shallow edges, down wind, either in clumps or as filaments.

What to look for

Outbreaks of blue-green algae often give off a characteristic musty odour. Blooms can vary in appearance from pale to bright fluorescent green, and may appear paint-like or granular in texture. Blue-green algae outbreaks are generally confined to areas of still water with little turbulence.