The mysterious discovery from the air of over 300 elephant carcasses, back in July of this year, sent alarm bells ringing to conservationists within Africa and much further afield.

Whilst over 300 deaths from an estimated population of 130,000 elephants roaming around Botswana was not deemed a serious threat to their existence, the very nature – the concentrated area and the closeness between the timing of their deaths did warrant serious investigation.  It has now been concluded after thorough tests and examinations that cyanobacteria was indeed the cause of these deaths.

Explaining why it was possible that other animals, apart from one horse, had not appeared to suffer the same fate, Mmadi Reuben,  Principal Veterinary Officer (Botswana Department of Wildlife & National Parks) hypothesised that the elephants using their trunks are drinking water from a lower level and therefore “closer to the silt where the anaerobic toxins are contained”.

What you need to know about cyanobacteria?

Cyanobacteria (commonly known as “blue-green algae”) are among the oldest and most primitive forms of life. They are found in fresh water lakes and rivers throughout the world, usually in low concentrations, and are not visible without the use of a microscope. However, when conditions are favourable, cyanobacteria cells can multiply and form cyanobacteria blooms or cyanobacterial mats. These may also accumulate to form surface scums in shallow inlets and bays and along the shoreline of lakes and rivers. Favourable conditions for cyanobacteria blooms include the right combination of warm temperatures,

sunlight, and low (or stable) river flows, or calm lake conditions. Cyanobacteria blooms are a natural phenomenon but human activities, such as taking water from rivers or adding nutrients to waterways, can increase the risk of blooms occurring. In particular, high levels of nutrients such as phosphorus and

nitrogen increase the risk of blooms occurring. These nutrients may reach waterways from sources such as fertiliser use, livestock, and sewage leakage or discharge in lake and river catchment areas.

What are the risks of cyanobacteria?

Blooms of cyanobacteria frequently are associated with a range of health risks. People can be exposed to cyanobacteria by drinking affected water, swallowing or inhaling droplets while swimming, or through direct skin contact. Where there are visible cyanobacteria blooms, scum collections, or mats, the risk of

exposure is much greater. The reported health effects of cyanobacteria are varied but include gastrointestinal symptoms (such as diarrhoea, vomiting, abdominal pain), headaches, fever, muscle aches, joint aches, vertigo, influenza-like symptoms, fatigue, drowsiness, sore throats, conjunctivitis (red eyes), blistering around the mouth, itchy skin rashes, hay fever-like symptoms, and various allergic reactions. Conditions such as hay fever, eczema and dermatitis may also worsen and exposure to cyanobacteria may trigger an acute attack of asthma. Cyanobacteria also often produce specific toxins that may damage the liver or are poisonous to the nervous system and these can be dangerous in high doses. Those at greatest risk of health effects are children and those with pre-existing medical conditions such as long-term liver or kidney disease.

The higher the concentration of cyanobacteria and cyanotoxins and the longer contact with the water, the more severe the symptoms are likely to be. Cyanobacteria surface scums and mats may contain very high concentrations of toxins and this may represent a specific risk to children who might be attracted to play with scums on the shoreline or in shallow areas of a lake or river.

Cyanobacteria health warnings

Regional Councils regularly test fresh water (rivers as well as lakes) for cyanobacteria. If high concentrations of cyanobacteria are found, the Medical Officer of Health will issue a Health Warning advising the public not to drink or use affected water and to refrain from any contact with areas of the lake or river that have cyanobacteria blooms or mats. When a health warning is in place, people are advised not to paddle, wade, swim, fish, or participate in any recreational activity that might involve significant contact with these cyanobacteria blooms, scums, or mats. Health warnings also advise people to keep their pets (e.g. dogs) and livestock out of areas of lakes or rivers affected by blooms.  Anyone suffering illness after contact with cyanobacteria blooms should seek medical assistance. Any illness in pets or livestock after contact with the river should be reported to the Medical Officer of Health.

When a Health Warning is issued, the District Council arranges signage at points of public access to the affected area(s). As it is not always possible to place signage at all parts of a river or lake that may be

affected the public should be vigilant to look for and avoid using any areas that have visible bloom activity, cyanobacteria scums or mats.

What do cyanobacteria blooms look like?

Cyanobacteria blooms usually result in the water becoming a dense blue-green or brown colour. Floating scums may be visible when cyanobacteria are present in high concentrations. Cyanobacterial mats may form in rivers and around lake edges where they most often cover submerged rocks, sand, gravel logs and

weed. Cyanobacterial mats are moss like in appearance, thickness and colour (dark brown/black) but have a much slimier texture and glisten when exposed to air. In shallow areas, the mats may appear bleached

and take on a golden brown colour. The mats are easily dislodged from the riverbed and form floating ‘rafts’. When cyanobacteria are present there is often a noticeable musty or ‘earthy’ odour.

How do you treat cyanobacteria?

The reduction of phosphate levels in a water body and its sediments through an application of Phoslock will therefore result in a significant reduction of blue green algae and the restoration of healthy ecological conditions which favour the growth of diatoms, green algae and macrophytes. For more information on Phoslock click here or contact one of Parklink’s friendly staff at