SummaryRead the full fact sheet
- Most algae are harmless and an important part of the natural ecosystem.
- Some types of algae are harmful to people and animals, and some can produce toxins which can cause serious illness.
- Where these harmful algae grow rapidly and accumulate in a water environment, it is known as a harmful algal bloom. It is difficult to tell the difference between a harmful algal bloom and a non-harmful algal bloom.
- Direct contact with algae can cause irritation to the skin, eyes, ears, nose and mouth. To be safe, people and pets should avoid water affected by algae.
- Do not use untreated algae-affected water for drinking, showering or washing. Boiling algae-affected water does not remove toxins.
- Algal toxins can gather in shellfish, crustaceans and the internal organs of fish. Where there is a harmful algal bloom, do not consume recreationally caught shellfish or crustaceans, and gut and gill fish prior to cooking or freezing.
What is an algal bloom?
Algae and cyanobacteria are simple organisms that live in the water. Algae and cyanobacteria can rapidly grow out of control, or “bloom,” when water is warm, slow-moving, and full of nutrients (for example, due to runoff containing fertilisers and sewage).
Blooms can occur in fresh water, marine water, and brackish water. Blooms can look like foam, scum, mats, or paint on the surface of the water. A bloom can change the colour of the water to green, blue, brown, red, or another colour. Some algal blooms may not be visible.
Algae and cyanobacteria can sometimes cause harm to people, animals, and the environment. An accumulation of algae which may be harmful to humans and animals is known as a harmful algal bloom. Harmful algae can be found in both marine (salt water) and freshwater environments.
Some types of algae can cause irritation and allergic reactions on direct contact, while others may also produce harmful toxins (poisons). Toxins produced by harmful algal blooms in a marine or freshwater environment can impact human and animal health. Seafood harvested from algae-affected water can also put our health at risk.
Harmful algal blooms will remain as long as there are favourable conditions – including warmth, sunlight and low flow rates.
Blooms can last from weeks to months – it is difficult to predict when they will clear.
Cooler, windy weather or increased water flow may reduce or stop algal blooms.
It is important to note, not all algae and cyanobacteria produce toxins, and not all blooms are harmful.
Harmful algae exposure symptoms
Contact with harmful algae can cause various illnesses and symptoms depending on the type of algae and your exposure.
Direct skin contact
Inhalation of fine spray or droplets from algae-affected water can cause mild respiratory effects and symptoms similar to . This most commonly occurs during recreational water-contact activities like swimming, water-skiing, jet-skiing and boating.
Drinking or consuming harmful algae
Pets and livestock can also be affected by harmful algae. If you think that your animals are unwell, see your vet.
How to avoid exposure to harmful algae in water
To reduce your exposure to algae-affected water:
- Look out for water that is discoloured or where visible scums are present. These scums are a build-up of algae that settles along the edge of the water – where you are more likely to make contact.
- Do not swim and avoid water sports where you may make direct contact with algae-affected water.
- Do not allow children to touch, swallow or swim in algae-affected water (and always supervise them when ). Children tend to have more sensitive skin than adults. They are also more likely to accidentally swallow or inhale harmful water which makes them more at risk to algae-related poisoning.
- Try to make sure children in your care are aware of the dangers of harmful algae.
- Follow advice on any information warning signage about harmful algal blooms.
- Avoid contact with the water until authorities advise there is no longer a risk.
- If you suspect that your local waterway is affected by harmful algae, contact the local waterway manager for further advice.
Remember, in some circumstances, water that is affected by harmful algal blooms may not be visible and may not smell any different. If in doubt, contact your local authority or find out more about the latest waterway warnings via .
What to do if you are exposed to algae-affected water
If you come into contact with algae-affected water:
- Immediately leave the water.
- Remove any traces of algae by thoroughly washing and rinsing your skin and hair, contaminated clothes and wetsuits in clean water.
- Wash and dry all clothing (including wetsuits) and equipment in clean water. Wetsuits used for water sports may increase the risk of rashes. Any algal material can get trapped inside the wetsuit and be in contact with the skin for long periods.
If you feel ill after contact, seek medical advice.
How to tell if a bloom is present
There are some ways to tell if waterways are affected by harmful algal blooms. These include:
- Look for warning signage and follow the advice given.
- Check the and websites.
- If there is no signage, look for discolouration and scums on the surface of the water.
- Consider whether the area is prone to harmful algal blooms.
- If in doubt, take a precautionary approach and follow the advice outlined in this fact sheet.
Keeping animals safe from harmful algae
Pets and livestock can be poisoned from contact with or ingestion of harmful algae. Precautions may include:
- Do not let animals swim in algae-affected areas.
- Avoid walks along banks where scums accumulate.
- Do not let animals drink algae-affected water.
- If you are a livestock owner, continuously check water supplies frequently for harmful algae, and keep livestock away from algal blooms.
Animal exposure to harmful algae – first aid
If an animal comes into contact with affected water or scums:
- Wash them thoroughly with fresh water before drying so they do not swallow algae while grooming their fur.
- If you are concerned about an animal’s health, consult a vet as soon as possible.
Seafood contaminated with algal toxins
Toxin levels can remain elevated in aquatic life for several weeks to months after an algal bloom has dissipated.
Eating seafood containing toxins can lead to serious illness.
Cooking or freezing the seafood does not destroy the toxins that cause illness.
When there is a harmful algal bloom:
• Avoid direct contact with algae-affected water.
• Do not consume recreationally caught shellfish and crustaceans.
• Gut and gill fish prior to cooking or freezing.
Seafood in areas without warning signs
Seafood can be affected even in places where there are no warning signs. This is because it not always easy to tell if a harmful algal bloom is present or whether there has been one previously.
Certain rivers and lakes in Victoria are particularly prone to harmful algal blooms. Some seafood can move in and out of algae-affected waters and may be caught in an area where a bloom is not apparent.
If you are unsure whether there is a harmful algal bloom, take a precautionary approach and follow the above advice.
Precautions for consuming fish contaminated with algal toxins
You can still catch and release, or harvest fish from algae-affected waters, as long as you take certain precautions:
- Wash the fish in clean water.
- Gill and gut (fillet) the fish prior to freezing or cooking.
- Put internal organs in the rubbish – it is likely that the fish has swallowed algal toxins, so don’t feed the leftovers to animals.
- Do not eat whole fish harvested from algae-affected waters.
When algal blooms die and start to break down, they use up oxygen in the water, which creates an environment that can suffocate fish.
If you see fish that are dead, dying or swimming erratically, do not touch or eat them.
Precautions for consuming crustaceans contaminated with algal toxins
Crustaceans (such as crabs, prawns, yabbies and crayfish) may also concentrate toxins in their internal organs.
Exercise caution when consuming recreationally caught crustaceans, especially when water quality is poor.
Do not consume recreationally caught crustaceans where there is a harmful algal bloom.
Avoid shellfish poisoning
Do not eat any (such as pipis, mussels, oysters, clams, cockles and wedge shells) from algae-affected water. Shellfish are more likely to accumulate dangerous levels of algal toxins and other harmful substances from the water.
You can become ill with shellfish poisoning if you collect and eat shellfish affected by toxins from a harmful algal bloom. Shellfish poisoning can cause serious illness and potentially death.
Symptoms of shellfish poisoning can occur from minutes to hours after eating affected shellfish. These may include:
Cooking or freezing the shellfish does not destroy the toxins that cause shellfish poisoning.
There is always a risk of illness from eating wild shellfish harvested where water quality is poor.
Harmful algae and water supply
Private water supply
- Sealing your water tank.
- Ensuring the pipes or fittings do not receive sunlight.
- Keeping up to date with information on private drinking water supplies on the .
Do not use untreated algae-affected water for drinking, showering or washing.
Boiling algae-affected water does not remove toxins.
Watering your garden with algae-affected water
Avoid using algae-affected water on your lawn and garden beds. It may affect the growth of plants, and poses a risk to anything that might contact the wet surface. Spray irrigation can also produce very fine, airborne water droplets which can lead to toxins being inhaled.
If there is no other water source, minimise water spray on your garden by using drip irrigation, soaker hoses or a watering can and avoid directly watering the edible portion of any plants.
Harmful algae and motor neurone disease (MND)
There is no consistent evidence that exposure to harmful algae causes in humans. Likewise, there is no evidence that people living in the vicinity of algae-affected water are at increased risk of developing the disease.
Where to get help
- Department of Health, , Victorian Government
- Department of Environment, Land, Water and Planning (DELWP), , Victorian Government
- Environment Protection Authority Victoria (EPA), , Victorian Government
- , Victorian Government
- Centers for Disease Control and Prevention (CDC), , United States
- Department of Environment, Land, Water and Planning, , Victorian Government