Cyanobacteria (blue-green algae) 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.
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 flowing rivers, the cyanobacteria species Phormidium forms thick mats of dark brown/black mats. Phormidium occurs naturally in rivers throughout Canterbury.
In the summer of 2007, thick mats of Phormidium were found in the Ashley River/Rakahuri. The lower reaches of the river had extensive areas where the thick, dark-brown/ black Phormidium sp. mats were present in the river and on the margins from SH 1 down to the estuary. At least 2 dogs died around this time, after licking or eating the algal mats. Analytical tests confirmed the presence of toxins, leading the local council to erect health warning signs at the river. Similar problems during the 2007 summer occurred in the Hutt River in the Wellington Region.
Cyanobacterial mats (Phormidium) are a dense dark brown/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 Phormidium 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.
The algae that commonly grow in lakes are a free-floating form (phytoplankton). Some species are cyanobacteria that have the potential to grow rapidly to form a high density of cells (bloom) and produce cyanotoxins. In Canterbury, Lake Forsyth/Te Roto O Wairewa forms a bloom of the cyanobacteria Nodularia in most summers. This alga produces the toxin Nodularin, which has been known to kill stock and dogs that are in contact with lake water during a bloom.
Algal blooms in lakes or still waters are commonly blue-green in colouration, but can also be red or yellow. They typically form thick scums on the surface, and may also develop foams at the water's edge.
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.
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.
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.
Dogs are particularly susceptible to poisoning from both mat-forming and free-floating cyanobacteria as they enjoy being in the water and can consume these algae 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 present in Phormidium mats 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.
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.
Dr Alistair Humphrey, Medical Officer of Health, says people swimming or showering in water with increased levels of algal bloom have been known to develop allergic reactions – asthma, eye irritations, rashes, blistering around the mouth and nose and gastrointestinal disorders including abdominal pain, cramps and diarrhoea.
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.
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.
No. Toxins are not removed by boiling, normal filter systems, or by adding household disinfectant.
Medical Officer of Health, Dr Daniel Williams has advised that, "Based on the advice I have received from experts on algal blooms and on test results there is no evidence of algal toxins at significant levels in reticulated water supplies in Canterbury or South Canterbury at present. Testing is ongoing. The known health risks are from direct contact with algae in river or lake water. Human or animal contact with affected rivers or lakes should be avoided."
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.
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 is 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.
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.
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.
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.
Avoid taking water from affected areas. If you do take water, stand away from sprays to avoid contact with, or inhalation of aerosols.
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