Blue-Green Algae Identification, Treatment and Risks–The Complete Guide

This article sources advice from multiple Australian Government websites, including the Government of Western Australian, the Government of Victoria and the Government of New South Wales. We’ve spliced together this official advice with our own advice; sourced from Scotty Tucker’s 20+ years of experience. You’ll know when we’re providing our own advice because the Australian Government statements will have “quotation” marks and our comments won’t. All sources are referenced at the end of this article. 

What is blue-green algae (cyanobacteria)? 

Blue-green algae is not algae but instead a type of cyanobacteria. The bacteria are microscopic but provide an algae-like appearance when the colony is large enough. This is where cyanobacteria get their name, cyano refers to the presence of photosynthetic pigments that often give them a blue-green appearance. Blue-green algae can grow in freshwater and marine water. 

“Cyanobacteria photosynthesise like plants and have similar requirements for sunlight, nutrients and carbon dioxide to grow and produce oxygen,” Australia’s Department of Climate Change, Energy, the Environment and Water says.  

“There are many different varieties of cyanobacteria. While often a green or blue-green colour, they can also be white, brown, blue, yellow-brown, or red. If conditions are suitable, cyanobacteria can increase to excessive levels and form visible ‘blooms’ which can lead to poor water quality and the potential for toxicity.” 

The dangers of blue-green algae 

People 

People can get very sick if they come into contact with blue-green algae. “There are no known antidotes for blue-green algae toxins once a lethal dose has been ingested,” The Victorian Fisheries Authority says.

“The symptoms in humans include rashes, headaches, fevers, gastroenteritis, seizures, respiratory failure,” Victoria’s Department of Agriculture says. “People may be exposed to these toxins through contact with the skin (for example, when swimming), through inhalation of water containing toxins (for example, when close to irrigation sprays) by swallowing contaminated water, or by eating fruit, vegetables or leaves with blue-green algae surface contamination.” 

We’ll add here that airborne particle transfer is worth noting if you use your water for irrigation. Spraying contaminated water onto your crops is one way to make people sick, but spray drift and airborne particles from contaminated water is also in need of consideration. Visitors and/or workers could get extremely sick if they breathe in contaminated air from sprinklers. Do not use any water suspected of contamination with blue-green algae as irrigation water if there is any risk of human contact with spray drift. 

Livestock and domestic animals 

“All animals, including people and farm dogs, are at risk of poisoning from blue-green algae,” WA’s Department of Agriculture says. 

In a separate article, WA’s Department of Agriculture recommends, “Livestock should be excluded from water supplies for the length of the withholding period or 14 days, whichever is longer.” 

Fish and aquatic life 

“[A blue-green] algal bloom also results in a loss of dissolved oxygen in the water causing the death of fish and other aquatic biota due to lack of oxygen,” The Victorian Fisheries Authority says. 

“People should not eat mussels or other shellfish collected from water affected by blue-green algae,” The Victorian Fisheries Authority says, because “most conventional treatments” like “boiling water” are “not effective in removing or deactivating the toxins.” 

Plants (irrigated with BGA-contaminated water) 

“Current evidence suggests toxins can be absorbed through the root system of plants” and “may remain viable on the surface of plant parts for long periods,” NSW’s Department of Primary Industries says.  

“Of most concern are the leafy vegetables, such as lettuces and cabbages, where water may pool on the vegetable surface and leave a dried, concentrated residue.”  

“Do not use a BGA-contaminated water source on edible plants if you have an alternative supply,” NSW’s Department of Primary Industries says.  

As mentioned earlier, we would go one step further and say, don’t use blue-green algae contaminated water on edible plants for any reason. Contaminated crops are a lot worse than lost crops. 

Testing for blue-green algae 

When to test 

WA’s Department of Agriculture recommends regular monitoring of farm water supplies for blue-green algae. “We recommend checking livestock and water supplies for blue-green algae daily in summer and autumn. Treat all algal blooms as possibly toxic to livestock and prevent stock access until the algae are identified and the level of toxin determined.” 

While this may seem excessive, we do recommend keeping an eye on your water during summer and autumn particularly, and if you notice any visual signs, then test your water. We have DIY test kits available that allow people to do this themselves in the field or at home. 

Victoria’s Department of Agriculture recommends farmers “inspect farm dams and water troughs regularly (at least 2 or 3 times a week) during hot, dry times of year.” 

Lab test  

WA’s Department of Agriculture recommends the following water sampling procedure to check if blue-green algae is present: 

“Avoid contact with the suspect water as acute skin and respiratory irritation can occur after short-term exposure to water containing cyanotoxins.  

  • Wear gloves and wash hands afterwards.  
  • Collect water in a watertight plastic or glass bottle with a wide mouth. A clean, disposable water bottle is suitable if no other containers are available.  
  • Clearly identify each sample container.  
  • Sample surface water where the bloom is most dense (100 millilitres is sufficient, no more than 500mL). Ensure sufficient space is left at the top of the container to allow mixing.  
  • Thoroughly wash the exterior of the bottle with clean water.  
  • Samples should reach the laboratory within 24 hours and be kept at approximately 4°C during transport (an ice brick and small esky is usually adequate).  
  • Do not freeze the water as algal cells may be damaged making identification difficult.” 

The downside to lab tests is they take several days for results to come back, which is a long time for a toxic waterbody. The results also cost hundreds of dollars which is unreasonable for testing at scale.

More importantly, standard algae identification tests provided by labs do not tell you if there are any toxins in the water or not. If you want the lab to tell you if toxins are present, you need to order an algal toxin test which takes over a week to get results and costs several hundreds of dollars.  

DIY field test kits 

In reality, a lab result is not going to help a farmer or field worker. We recommend you do a preliminary test using one of our blue-green algae test kits instead. The test provides enough of an indication whether your water is toxic or not, and it allows you to see results in 10 minutes, not several days. The test detects 11 hepatotoxins common in blue-green algae, and the best part, it tests for toxins, rather than the cyanobacteria itself. So, you have an idea of toxins even after the cyanobacteria has gone. 

Pictured: blue-green algae test kit

Treating blue-green algae 

Toxins released at BGA death 

“Blue-green algae can release toxins into the water, and those toxins can be present for many months after treating the algae,” WA’s Department of Agriculture says. “When blue-green algae is killed, toxins in the cells are released into the water, increasing the risk of poisoning. Sun-dried blue-green algae can remain toxic for up to five months.”  

This is a key point: you can’t visually see these toxins. The algae might be gone but the toxins will be there for a while after. Therefore, after treatment of blue-green algae, we recommend testing your water several times to make sure the water is clear of toxins. We sell multiple test kits for this reason. Bulk orders are also available. 

Chemical algaecide treatment warning 

Algaecide can make the above situation worse. WA’s Department of Agriculture says, “Several chemicals can be used to treat blue-green algae growth”, although they also state, “chemical treatment of algae can cause a sudden release of toxin, which can persist for several days.”  

“Any agent that kills blue-green algae will result in an initial increase in toxin levels as the algae die and more toxin is released into the water supply,” Victoria’s Department of Agriculture says. 

“If an algicide is used, water should be monitored for toxin levels, or all animals should be excluded from the water supply for at least 28 days after its use (use as per manufacturer guidelines), because the water can remain toxic for that period.” 

“For this reason, algicides do not necessarily provide a short-term solution to the lack of an alternate water supply,” Victoria’s Department of Agriculture. 

Natural Treatments 

This is a very important point, not just for testing your water after treatment, but also as a case for ramping up microbial bacteria in the water as part of treatment. A product like Biostim achieves this by boosting the populations of beneficial aerobic bacteria.  

Biostim also helps prevent blue-green algae showing up in the first place. We explain below. 

Preventing blue-green algae 

“It is possible to reduce the likelihood of blue-green algae developing in farm water supplies,” WA’s Department of Agriculture says. “Regular sampling of susceptible supplies will help identify the early stages of algae growth, and early treatment is much more successful in preventing blue-green algae growth and poisoning.” 

The Department of Agriculture also states one key cause of blue-green algae blooms is “insufficient microscopic organisms that feed on algae and keep algal levels under control”. 

Probiotics like Biostim increase these populations of “good” microscopic organisms who feed on algae and compete with them for resources. In other words, a monthly dose of Biostim creates conditions in your water that make it very difficult, if not impossible, for blue-green algae to return.  

Sources 

  1. ‘Cyanobacteria (blue-green algae) and water quality’, Department of Climate Change, Energy, the Environment and Water 
  1. ‘Managing blue-green algae on farms in Western Australia’, Department of Agriculture, Government of Western Australia  
  1. ‘Blue-green algae poisoning in livestock’, Department of Agriculture, Government of Western Australia 
  1. ‘Sampling procedure for toxic algae’, Department of Agriculture, Government of Western Australia 
  1. ‘Managing blue-green algae in farm water supplies’, Department of Agriculture, Government of Victoria 
  1. ‘Irrigating with blue-green algae affected water’, Department of Agriculture, Government of New South Wales 
  1. ‘Blue-green algae’, Victorian Fisheries Authority 
  1. ‘Blue-green algae’, Department of Agriculture, Government of Victoria