Blue-green algae (cyanobacteria) are a type of microscopic, algae-like bacteria which inhabit most aquatic systems including streams, lakes, estuaries and the sea. There are many different species (toxic and non-toxic) and hot sunny days, increased nutrient levels and still weather conditions can provide optimal conditions for them to flourish – rapid growth can create a ‘bloom’ on the water’s surface. Blooms mostly occur in warmer weather (spring, summer and early autumn), but they can happen any time if conditions are favourable.

Blue-green algae can affect water quality, however we have treatment processes in place to ensure the continuous provision of safe and reliable water. Sometimes higher levels of blue-green algae can create an ‘earthy’ taste or odour in treated water, but the water remains safe to drink – we’ll always let you know if that changes.

All drinking water supplied to customers meets the Safe Drinking Water Act 2003 and the Australian Drinking Water Guidelines. We continually monitor and assess the water quality, and samples are regularly sent to an independent laboratory for testing. We also work closely with Goulburn-Murray Water, which manages a number of waterways from which we source water.

Blue-green algae in the Yarrawonga Weir in 2020.

Current blue-green algae detections

Blue-green algae has recently been detected in Lake Nillahcootie and in the Broken River system. The regional algae alert has been extended by Goulburn Murray Water to include the Broken River to Sheppartn, as well as the Broken Creek from Caseys Weir to Katamatite.

Goulburn Valley Water's water treatment processes are effective at removing the blue-green algae and thier metabolites, and we continue to monitor the raw water conditions.  

There is currently no risk to our drinking water supplies from the expansion of the algae alert and Shepparton’s town water remains safe. This is also the case for Nathalia’s drinking water supply from the Broken Creek. Katamatite and Numurkah water treatment plants' raw water is sourced from the Murray Valley Irrigation District and is unaffected by the alert.

More information can be found at Goulburn-Murray Water's website

Regulated (non-potable) supplies

Goulburn Valley Water supplies several towns with non-potable (non-drinking) water supplies. We recommend these customers have an alternate supply of drinking water.

Potable (fully treated) supplies

We regularly monitor for blue-green algae in our raw water supplies. Our water treatment plants remove algae and dissolved compounds as part of the treatment process before the water reaches your taps.

FAQs - blue-green algae and water treatment

The majority of our raw water is sourced from the Goulburn and Murray Rivers, their associated tributaries, and irrigation channel systems managed by Goulburn-Murray Water. In recent years, water storages on both the Goulburn and Murray River systems have experienced blooms of blue-green algae that have impacted on the water quality.

What are blue-green algae?

Blue-green algae are not algae, but bacteria that are a natural part of aquatic systems. They come in a range of shapes and sizes and can be free floating in the water or live on rocks and vegetation at the bottom of waterways. Although the single cells are microscopic, some species of blue-green algae form colonies or filaments that can join and are visible to the naked eye; forming pea shaped masses, or paint like algae slicks at the water’s surface in many unusual colours including green, blue, red, brown, white or yellow. At other times, the sheer volume of blue-green algae in a waterway may turn the water a deep green but not produce surface scums.


How can blue-green algae affect drinking water?

Different species can be toxic or non-toxic and can produce taste and odour causing compounds such as geosmin and 2-methylisoborneol. These compounds have a strong, unpleasant earthy or musty taste and odour that can be detected at extremely low levels, as low as 0.00001 mg/L. In comparison, chlorine can generally be tasted between 0.1 and 0.4 mg/L. At high levels, it can be difficult to remove all taste and odour from the treated water.  

Blue-green algae and the water treatment process

We use many treatment technologies to remove algae, particulates, and dissolved compounds from surface water. To remove compounds that cause taste and odour we use activated carbon (powdered or granulated), which is added pre-treatment and then removed along with the algae cells and other dirt as part of the filtration processes. Activated carbon is extremely porous and absorbs taste and odour compounds onto its surface.

Even though not all toxic species of blue-green algae will produce toxins, we proactively use a range of water treatment processes to remove any potential toxins and ensure water is safe to drink This includes:

  • managing our access points to raw water sources
  • pre-treating with carbon
  • removing algae cells intact
  • using coal and fine sand filters
  • oxidising the water to destroy any toxins that might be present.

How long will blue-green algae impact on water quality?

There is no way to predict how long a bloom might last and there is no easy fix.

Blue-green algae grows when a combination of favourable conditions, including temperature, light and nutrients are present. Blooms develop rapidly when the conditions are right, followed by a stable period called the plateau phase after which the cells start to die off. Once the bloom has plateaued, it can remain for weeks or months if environmental conditions are still right. Compounds causing taste and odour can remain in the water for extended periods of time, even after the bloom has died off. This means some people may notice lingering taste and odour in the drinking water for quite some time.

Is there anything I can do to improve the taste?

We know taste and odour can be frustrating – we’re sorry. Some people have reported that putting water in a jug in the fridge can help with any taste and odour issues. You could also consider adding lemon or fruit wedges (orange, mint, watermelon, etc) to help.

I have a concern or enquiry about water quality, who do I contact?

While we’re always working to optimise our treatment processes to improve the taste and odour, blue-green algae can be unpredictable. Sometimes these taste and odour events occur without our knowledge, such as when a bloom occurs extremely high up in the water catchment and releases taste and odour compounds that move downstream while the blue-green algae remains behind.

If you’re a Goulburn Valley Water customer and you notice a change in your water supply or you have an enquiry, please contact us on 1800 454 500 at any time, or report it online.

If you are supplied by Goulburn-Murray Water (irrigation or stock and domestic supplies) you can find more information at their website.

Recreational warnings

Recreational warnings are issued by Goulburn-Murray Water and Water NSW and do not relate to the quality of drinking water supplied by us. Recreational users should be aware of alerts which can be found at:

Blue-green algae in the Goulburn River in 2019.

Blue-green algae in an irrigation channel in 2019.