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| Last Review/Updated: August 12, 2003 |
What are Algal Blooms and Blue-green Algae? - When microscopic plants
called algae become so thick that they make lake water look like pea soup, the
condition is called an algal bloom. Among the more common types of algae producing
blooms are the blue-green algae. More than 100 species of blue-greens have been
recorded in Alberta, although the most troublesome blooms in central Alberta
are caused by only three of these: Aphanizomenon flos-aquae, Microcystis
aeruginosa, and Anabaena flos-aquae. Associated with blooms of these species
is the threat of toxicity or poisoning. Intense and widespread toxicity has
not occurred in Alberta lakes, although some have been severe enough to cause
the death of domestic animals, waterfowl and other wildlife.
Why Do Blue-greens Make Lakes Toxic? - Blue-green algae have been known to be a cause of toxicity in lakes, ponds and dugouts for over 100 years, since the first poisoning cases were recorded. Cases of animal poisonings have occurred all over the world, including Alberta. Continuing research has shown that blue-green algae can produce different types of toxins or poisons. Only a few of the toxin-producing blue-green species are normally abundant in central Alberta lakes. Fortunately, these few species are toxic only on occasion because each species may have many strains and only some strains produce toxins. Toxins may be released as soon as they are formed or upon the death or decomposition of the algae.
Toxicity due to blue-green algae can only occur if there is a blue-green bloom dominated by the toxic strains of the bloom species. Toxic strains and non-toxic strains of a bloom may occur at the same time in a lake, and as a result some parts of the lake could become toxic while others could remain safe. Toxicity in a lake is normally temporary, lasting only as long as the bloom or signs of the bloom persist.
Can
Toxicity be Predicted? - The reason why toxic strains suddenly become more
dominant than the nontoxic strains is not known. Consequently, toxicity due
to blue-greens is even less predictable than the blue-green blooms themselves.
Lakes that have never had a problem can suddenly become toxic. Conversely, lakes
that have shown toxicity in the past may never show it again. Careful vigilance
of lakes where blooms have occurred is the best approach to identify a problem.
How Do Blue-green Toxins Affect Animals? When a lake becomes toxic as a result of a blue-green bloom, the only sign of a problem may be dead waterfowl or wildlife along the shoreline. Occasionally, domestic animals such as cattle or dogs may be poisoned if they have no other source of drinking water.
Strains of blue-green algae produce a number of toxins that can be classified into two groups according to their effects on animals. Neurotoxins affect the nervous system and cause a rapid death, often within 30 minutes, due to paralysis and respiratory arrest. The second group, hepato-toxins, affect the liver and cause a slow death, up to 36 hours after drinking the water. Common symptoms are lethargy, pallor, hemorrhaging, and swelling of the liver.
Several toxins may be present at the same time and the symptoms may vary or lack clear definition. The amount of toxic water that will kill an animal is generally proportional to the size of the animal. Old, very young, sick or weak animals may have lower tolerance levels and will be poisoned with much smaller amounts.
How Do Blue-green Algal Toxins Affect People? - Humans are just as susceptible
to blue-green toxins as animals, but it is unlikely that people would voluntarily
drink much lake water during a bloom because of the objectionable appearance
and odour of the water.
This explains why there are no records of toxicity causing death in humans. However, people may suffer acute discomfort after ingesting or contacting toxins. Symptoms may include fever, headache, dizziness, stomach cramps, vomiting, diarrhea, skin and eye irritations, sore throat and swollen lips. Symptoms seldom persist for more than two or three days. Children may be more intensely affected because they spend more time in the water than adults and they may accidentally ingest contaminated shoreline water. They also may have lower tolerances than adults to the toxins.
How is Toxicity Determined? - Determining the presence of toxins in lakes is not a routine procedure. If the death or distress of animals is observed near a lake, several methods, each of which has limitations, can be used to decide whether algal toxicity is implicated.
The presence of potentially toxic blue-green species can be determined microscopically, but this technique cannot distinguish toxic from nontoxic strains because the strains look alike. A standard mouse bioassay is the fastest way of determining the presence of toxins. Laboratory mice receive injections of lake water or stomach fluids from the dead animals. The survival time of the mice is a measure of toxicity.
Definitive chemical analyses for algal toxins that affect the nervous system can be performed by Alberta Agriculture within a matter of hours. The analysis for the toxins that affect the liver takes more than two days and is complicated because the toxins are difficult to differentiate from some other chemicals.
What Precautions Can You Take?Who Can You Contact?
If you suspect a problem related to an algal bloom, or if you find dead animals
in or near a lake, contact:
For more information on this issue read about Algal
Blooms.
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