Friday, 5 August 2011

Blue Green Algae - What are the Dangers ?

Excessive blue green algae has been a problem in various coastal and river estuary areas of France for a number of years.  Although the algae is harmless while at sea, the danger is from the hydrogen sulphide gas that is given off by the algae as they decompose when they form in large quantities and when they end up out of the water and decaying on the beach.

So far this year there have been deaths of 30 wild boar in an estuary in Brittany ( and ( and this month the deaths of two dogs on the Tarn River in the Lozère region in the South of France (

Blue-green algae (cyanobacteria) are natural inhabitants of many inland waters, estuaries and the sea. In fresh waters, they are found in suspension and attached to rocks at the bottom of shallow water and along the edges of lakes and rivers.  In small numbers they are important and useful parts of the aquatic ecosystem. They convert energy from sunlight into chemically useful forms, liberate oxygen into the water, take up minerals and produce substances which enter and support food chains.

Like other floating plants, blue-green algae need nutrients to grow, particularly nitrogen and phosphorus. If the water is enriched with nitrogen and phosphorus, for example from excess farm fertilisers ending up in the water and if there is also enough sunlight , a suitable water temperature and the water flow is not too hight then the numbers of blue-green algae can become excessive. Such extensive growths are sometimes referred to as BLOOMS.

Such algal blooms sometimes cause foaming on the shore-line and during calm weather they can form a SCUM. They may also use up so much of the oxygen in the water that this can be a problem for fish.
Depending on the exact species involved, scums may appear blue-green, grey-green, greenish-brown or occasionally reddish-brown.

All blue-green algae contain blue pigment in addition to green chlorophyll pigment, although the blue colouration cannot normally be seen in the living cells.  However, when blooms and scums decay, the pigments are released and a bright blue appearance may persist for days or weeks.

Blue-green algal scums can form quickly on calm days, but can be dispersed rapidly if wind and wave action increases. For reasons which are not yet fully understood, bloom and scum forming blue-green algae in freshwaters, brackish water and seawater are capable of producing TOXINS. These toxins have caused the death of wild animals, farm livestock and domestic pets in many countries.  In humans, rashes have occurred following skin contact, and illnesses have occurred when blue-green algae have been swallowed. Blue-green algal blooms and scums are not always toxic but it is not possible to tell from its appearance whether or not a bloom or scum is harmful. It has been estimated that 50% of blooms could be toxic. Waterusers, particularly children, farmers and pet-owners should treat all blue-green algal blooms and scums with caution.

A massive beach cleaning effort operates on many beaches in the Brittany area and in some places it takes up a third of a town's budget just to clear this stuff. The men or women who operate the machines wear gas monitors at all times and if these alert the to high gas levels they have to stop work. ( It is a problem which towns do not want to shout too much about in case this would then affect the tourist trade, but there were recent calls for the French national government to help to tackle the problem.

Excessive nitrates used as fertilisers by farmers are blamed as these run off the fields and into water courses. The algae then feed on these nutrients. A solution may be a move to more organic or natural farming methods eg a return to leaving fields for a year of fallow with clover grown to add nutirents to the soil perhaps ? Raised water temperatures perhaps from global warming may also be an additional factor.

Could children be in danger ? Well yes, possibly, as small children are the same size as some of the dogs who have died. So it is important to take note of any warning signs and maybe avoid areas with excessive seaweed or algae unless you know how to identify the dangerous types. In the Lozère area they have recommended that the smallest children do not bathe in the area where the dogs died in the Tarn river. More information should be available in the locality where you are holidaying. However lets hope this problem gets sorted out soon !

NEWS UPDATE - 10th August 2011 - The French Minister for Ecology, Nathalie Kosciusko-Morizet, has ordered the closure of all beaches with green algae, which cant be cleaned within 24 hours.

Have you come across any algae while on holiday or did you come across warnng notices ? Let us know what your experiences were and would it make you avoid holidaying in certain areas ?
For further information about algae :

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