Toxic Algae in our Waterways

During extended summer low flows some naturally-occurring blue green algae (cyanobacteria) can produce toxins which, if consumed in high enough quantities, can cause trauma or death. In Tasman District there have been no cases of human sickness or death due to toxic algae and only one suspected case of a dog death. Dogs are most vulnerable to these toxins because they will drink from rivers and consume algae either attached to the bed or floating.

What is Blue-Green Algae?

Blue-green algae (cyanobacteria) are an ancient group of organisms with characteristics in common with both bacteria and algae.

Blue-green algae are widespread in many lakes and rivers in New Zealand, and are found in a wide range of water quality conditions, including relatively 'clean' waters.

A potential toxin-producing Cyanobacteria called Phormidium

Under favourable conditions, blue-green algae cells can multiply and form blooms in lakes or thick mats attached to river and stream beds.

Some species produce natural toxins called cyanotoxins which are a potential threat to people and animals if present in drinking water or if people and animals come into contact with the water during recreational activities.

In the summer of 2008/09, the first suspected dog death in Tasman District was recorded.

During much of the summer rivers such as the Waimea, Wangapeka, Motueka, and Takaka, often have thick, dark-brown/ black mats of Phormidium sp. covering up to 20% of the bed surface.

Cyanobacteria floating 'raft' in the Hutt River

What do mat-forming blue-green algae look like?

Blue-green algae mats are a dense dark green/black colour and are typically found on stable substrate such as large rocks, stones and cobbles and stones. These mats are soft to the touch and can be over 3mm thick and jelly-like.

They may have a 'dreadlocks' appearance in slow moving parts of the river and may come loose from the riverbed and form floating 'rafts', which become caught in other debris in the river. When the blue-green algae mats die and dry out they become light brown or white in colour.

The more brightly coloured long filamentous green algae that are commonly found in rivers and streams are harmless algae that do not produce toxins.

What causes blue-green algal blooms?

The presence of extensive mats of blue-green algae is linked with environmental conditions conducive to their growth. Favourable conditions include the right combination of warm temperatures, sunlight, low or stable river flows, and nutrients. The occurrence of mats or algal blooms is a natural phenomenon but human activities, such as taking water from rivers or adding nutrients to waterways, can make things worse.

Are blue-green algae always toxic?

No. There are several species of blue-green algae (cyanobacteria), that may or may not be toxic, depending upon prevailing environmental conditions. However, if potentially toxic blue-green algae are present in large numbers, you should presume that the water may be unsafe for contact recreation or consumption.

Some algae have toxins in their cells, and can be harmful if they are consumed. Such algae present a risk to dogs which may eat algal mats, or ingest algae when they drink water from a watercourse. Other blue-green algae may release toxins into the water surrounding them, which can affect those that contact or drink the water.

How do I know if the water contains toxin-producing blue-green algae?

Identification of blue-green algae requires a microscope, and its presence alone does not confirm cyanotoxin production, as not all species produce cyanotoxins and not all toxic species produce toxins continuously. Cyanotoxins are identified using a range of laboratory tests. The factors that trigger toxin production in blue-green algae are not completely understood.

What risk do the cyanobacterial mats/toxin-producing blue-green algae pose to stock and domestic pets?

Dogs are particularly susceptible to poisoning from mat-forming blue-green algae as they enjoy being in the water and can consume these mats intentionally or by accident. Livestock are also at risk from poisoning from cyanotoxins and should be provided with alternative drinking water. Symptoms of poisoning in animals include; lethargy, muscle tremors, fast breathing, twitching, paralysis, convulsions.In extreme cases death can occur within 30 minutes after signs first appear. If you are concerned, contact a veterinarian immediately.

Who should I call if I think my animal is sick?

If you are concerned about your animals, you should contact a veterinarian immediately. You or your vet can report any animal illness resulting from contact with the blue-green algae to your local council.

What are the health risks to humans from toxin-producing blue-green algae?

People can be exposed to the toxins by swallowing or drinking the water, skin contact with the water, and the consumption of fish or shellfish from affected waters. Swallowing water containing the toxins can lead to vomiting, diarrhoea, abdominal pain, cramps, and nausea. Skin contact with the toxins can cause irritation of the skin, eyes, nose, and mouth, which may appear as an itch, redness, and dermatitis.

Conditions such as asthma, hay fever, and eczema or dermatitis may also worsen. Toxins can also affect the liver and the nervous system. Those at greatest risk of a reaction are children, pregnant women, elderly, and those with pre-existing medical conditions.

Any reaction depends on the type of cyanobacteria, the type of cyanotoxins present, and the concentration of the toxin in the water.The higher the concentration of blue-green algae and cyanotoxins and the longer contact with the water, the more severe the symptoms are likely to be.

Who should I call if I think I have experienced a reaction?

If you think you have experienced a reaction after exposure to water containing blue-green algae, see your GP and tell him or her that you think you have been exposed to potentially toxic blue-green algae. Ask your GP to notify Nelson-Marlborough Public Health of any people with possible reactions.

Is it safe to drink water containing toxin-producing blue-green algae?

No. Toxins are not removed by boiling, normal filter systems, or by adding household disinfectant.

What do I do if my water supply comes from a stream?

Check your intake (and also upstream) for the presence of blue-green algae mats and contact your local council if you think your water supply may be affected.

Is it safe to swim in water with toxin-producing blue-green algae?

No. You should avoid any skin contact with the water and avoid swallowing the water.The higher the concentration of blue-green algae and cyanotoxins and the longer time in the water, the more severe the symptoms are likely to be.

Can I eat fish or shellfish from water with toxin-producing blue-green algae?

No. Eating mussels and other shellfish from affected areas should be avoided as they can concentrate the cyanotoxins produced by the blue-green algae. If you choose to eat fish from waters containing toxic blue-green algae, you should eat them in moderation. Avoid eating the liver and kidney of the fish, as this where accumulation of cyanotoxins may be the greatest. Fish may taste earthy. Avoid contact with the water while fishing and wash all fish in clean water.

Is it safe to boat or canoe in water with toxin-producing blue-green algae?

How safe boating and canoeing are depends on the amount of direct contact with the water. If you swallow the water or your skin is in contact with the water while boating or canoeing, you are at risk from a reaction to any cyanotoxins that may be present. The higher the concentrations of blue-green algae and cyanotoxins and the longer that people are in contact with the water, the more likely a reaction is to occur. Wash boats or canoes and life-jackets down with clean water after use.

Will wearing a wetsuit protect me?

No, wearing a wetsuit will not protect you. The blue-green algae may accumulate in the collar and cuff areas of wetsuit and rub against your skin. This may cause a strong skin reaction in these areas. If you do choose to wear a wetsuit and go into the water, take care to rinse any blue-green algae off the wetsuit with fresh water.

Can I water my garden with water that contains toxin-producing blue-green algae?

Yes. Fruit and vegetables do not appear to absorb the toxins. However, fruit and vegetables should be washed well in clean water as the blue-green algae may form a residue on the surface, which can remain toxic even when dry.

Can I use water containing toxin-producing blue-green algae to put out fires?

Avoid taking water from affected areas. If you do take water, stand away from sprays to avoid contact with, or inhalation of aerosols.

Where can I get more information?

Contact Council with queries relating to animals and water supply
Contact Nelson-Marlborough Public Health with queries relating to human health, ph 03 546 1541