Catchment Water Health
 Wimmera River near Horsham |
Lakes and waterways in the Wimmera River can potentially become enriched with nutrients, mainly nitrogen and phosphorus. This may have occurred naturally or as a result of human activities such as farming, urban development and forest clearing. Increasing the nutrient load to the aquatic environment can result in a dramatic increase in the production of algae and other aquatic plants. This can, in turn, lead to a number of significant water quality problems including fish kills, scums, offensive taste and odours, toxins, corrosion of supply system and tanks, filter clogging and water treatment problems.
In low numbers, algae are not usually a problem. In fact, they are an essential part of a healthy body of water as they produce oxygen and are themselves a source of food for certain aquatic fauna. Also, some types can convert nitrogen gas into forms that improve the fertility of the water.
Blue-green algae are of particular concern as they can produce toxins that can be poisonous to humans and animals. Under favourable conditions, outbreaks of blue-green algae can develop into major blooms presenting significant health risks to regional communities.
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 (with 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 that 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 algae can range in hue 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.
Farmers are often alarmed when they see any form of algae in their water supplies but, while other types may be a nuisance, it is usually only certain types of blue-green algae - including Microcystis, Anabaena and Nodularia - that are a cause for concern.
Algal blooms in general, and those of potentially toxic blue-green algae, affect water quality by causing peculiar tastes and odours, discolouration and unsightly scums. As the bloom dies, the decaying algal cells reduce the oxygen concentration in the water causing oxygen stress and often even death to other aquatic inhabitants, particularly fish.
Blue-green algae have some characteristics not shared by other algal groups. Among the main adaptive features that enable them to exploit the environmental conditions include that their cells hold small pockets of gas or "vesicles". These vesicles form and collapse intermittently, thereby acting as buoyancy regulators, enabling the algae to move up and down water columns to seek maximum light and utilise the nutrients available at lower depths. Some are capable of fixing atmospheric nitrogen, which gives them an advantage over the other algae, especially when there is a short supply in the water. They can take in phosphorus in very high amounts and store the excess for use when supplies are short. Blue-green algae also has the ability to utilise inorganic ions such as bicarbonates as sources of carbon dioxide, even when the pH is high and carbon dioxide is in short supply.
There is no single reason why blue-green and other algae have become such a problem in recent years, particularly in summer, but some contributing factors are:
- algae thrive on nitrogen and phosphorus and these chemicals have entered water systems in large amounts following their use or perhaps over-use in commercial, domestic and agricultural activities (eg: top dressing, dairy washing, abattoirs).
- the warmer temperatures and light intensity experienced in the water during summer provide favourable conditions for growth.
- in summer, stratification of water results in higher temperatures in the upper levels. Also, nutrients tend to be released from sediments providing nourishment for algae; relatively still and stagnant waters favour their growth.
For more information regarding how to identify algae blooms, prevention and treatment, or to see updated algae alerts see the DSE website (external link) and statewide Victorian Resources Online website.
© The State of Victoria, 1996 - 2012.
This document was last reviewed on 08/12/2009