Blue-green algae are naturally occurring bacteria found in rivers, reservoirs and water storages. Hot weather and still water provide ideal conditions for these organisms to grow prolifically, causing a ‘bloom’.

These blooms can affect water quality and contribute to taste and odour changes, and occasionally the presence of toxic compounds.

A sudden change in water colour overnight, due to the appearance of a mass of vivid green algae (scum) floating to the surface of the water.

Scums can be green, blue-green or khaki green, and can turn brown/green or white once dying off. They may appear at dusk or dawn and disappear during the day.

There may be a strong earthy smell or, if the bloom is breaking down, it may produce a strong rotting smell.

Some species of blue-green algae (BGA) in large numbers, or ‘blooms’, can produce toxins and can pose serious health implications for humans, animals and birds drinking or coming into contact with the water. While not all blooms are toxic, they should be treated as toxic until the water has been tested.

Typical symptoms for people who have ingested water contaminated with BGA include gastroenteritis, diarrhoea and vomiting. Avoid all contact with BGA, including skin contact.

Livestock are also at risk of poisoning by BGA unless alternative drinking water supplies are provided, although livestock deaths are relatively rare. Livestock productivity will be reduced with milder cases of algae poisoning.

Very rarely, blue-green algae (BGA) can pose a risk to the safety of drinking water if they produce toxic compounds.

However, Coliban Water monitors the water for the presence of toxins, and has treatment processes in place to remove toxins when they are present.

Currently, the big issue we are facing with the presence of BGA is the production of taste and odour compounds, such as geosmin.

This is an aesthetic issue. Treated drinking water that contains geosmin poses no health threats, and the water is safe for all drinking, bathing and cooking purposes.

Recent wet weather and flooding, followed by warmer temperatures, is contributing to higher concentrations of blue-green algae in the Murray River and its tributaries.

We use a number of treatment barriers and other processes to ensure the algae do not affect the safety of your drinking water.

Coagulation and filtration are used to remove algal cells from the water and ‘powdered activated carbon’ (PAC) removes any toxins that may be present.

Extensive testing is conducted on treated water to ensure it meets the health-based parameters set in the Australian Drinking Water Guidelines and the Safe Drinking Water Act 2003.

Recreational warnings may be issued by Coliban Water for our reservoirs or by other water authorities during algal blooms, advising people to avoid contact with the water.

This is important in these recreational settings, however, recreational warnings do not apply to the quality of the drinking water supplied by Coliban Water, which is treated.

Our water treatment plants have processes in place to treat the water so it can be safely consumed.

It’s difficult to say how long each blue-green algae bloom will last.

Once an algal bloom subsides, there may still be elevated levels of geosmin in the raw water we source for treatment, which could last for some time.

However, as the weather cools and the quality of the raw water improves, incidents of algal blooms and elevated geosmin levels typically decrease, improving any taste and odour issues in the drinking water.