Toxic algae - Cyanobacteria

Toxic algae - Cyanobacteria

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What are cyanobacteria?

Benthic cyanobacteria

Cyanobacteria are an ancient group of organisms with characteristics in common with both bacteria and algae. Cyanobacteria 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. Cyanobacteria are sometimes called blue-green algae, although they are usually a dark green/brown or black colour.

What is the problem with cyanobacteria?

Under favourable conditions, cyanobacteria 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 2005/06, thick mats of cyanobacteria were found in some reaches of the Hutt, Mangaroa, Wainuiomata, Otaki, Waikanae and Waipoua rivers. The Hutt River was affected for much of the summer, with extensive thick, dark-brown/ black mats of Phormidium sp. present on the river margins in the Boulcott-Avalon area during a period of extended low river flows in November 2005. At least five dogs died around this time, after coming into contact with the algae at the water?s edge. Analytical tests confirmed the presence of toxins, leading Regional Public Health and local councils to erect health warning signs restricting access to affected rivers in the region over the summer.

Since 2005/06 there have been a further seven dog deaths from dogs coming into contact with cyanobacteria in rivers in the Wellington region.

Cyanobacteria floating 'raft' in the Hutt River at Silverstream Bridge

What do mat-forming cyanobacteria look like?

Cyanobacterial mats are a dense dark green/black colour and are typically found on stable substrate such as large rocks, stones and cobbles and stones. 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 cyanobacterial 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.

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What causes cyanobacteria algal blooms?

The presence of extensive mats of cyanobacteria 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 cyanobacteria always toxic?

No. There are several species of cyanobacteria, that may or may not be toxic, depending upon prevailing environmental conditions. However, if potentially toxic cyanobacteria 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 cyanobacteria 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 cyanobacteria?

Identification of cyanobacteria 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 cyanobacteria are not completely understood.

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

Dogs are particularly susceptible to poisoning from mat-forming cyanobacteria as they enjoy being in the water and can consume these mats intentionally or by accident. Livestock are also at risk from poisoning from cytotoxins and should be provided with alternative drinking water. Symptoms of poisoning in animals exposed to the type of cyanotoxins identified in the Hutt River and Waikanae River during 2005/06 included; 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 cyanobacteria to your local council.

What are the health risks to humans from toxin-producing cyanobacteria?

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 cyanobacteria 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 cyanobacteria, see your GP and tell him or her that you think you have been exposed to potentially toxic cyanobacteria.Your GP has been asked to notify Regional Public Health of any people with possible reactions.

Is it safe to drink water containing toxin-producing cyanobacteria?

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 cyanobacterial 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 cyanobacteria?

No. You should avoid any skin contact with the water and avoid swallowing the water.The higher the concentration of cyanobacteria 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 cyanobacteria?

No. Eating mussels and other shellfish from affected areas should be avoided as they can concentrate the cyanotoxins produced by the cyanobacteria. If you choose to eat fish from waters containing toxic cya­nobacteria, 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 cyanobacteria?

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 cyanobacteria 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 cyanobacteria 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 cyanobacteria off the wetsuit with fresh water.

Can I water my garden with water that contains toxin-producing cyanobacteria?

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

Can I use water containing toxin-producing cyanobacteria 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 your local council with queries relating to animals and water supply
  • Contact Regional Public Health with queries relating to human health, Regional Public Health, Ph (04) 570 9002