Blue-green algae are natural inhabitants of many inland waters, estuaries and the sea. Although referred to as algae they are, in fact, a type of bacteria (known as cyanobacteria) with the ability to use the sun’s energy to make food in the same way that many plants do. They may be found in suspension, attached to rocks and other surfaces at the bottom of shallow waterbodies and along the edges of lakes and rivers. The term blue-green algae includes a number of different species.
All species of blue-green algae need nutrients - nitrates and phosphates - to grow. If the water is enriched with nutrients and we have calm, sunny and warm weather conditions, then the growth may become excessive resulting in algal blooms.
These algal blooms cause the water to appear discoloured green, blue-green or greenish-brown and some species can produce a musty odour. When the blooms die they break down, using up oxygen in the water and cause problems for other aquatic life such as fish. In calm, warm weather some bloom-forming species will rise to the water surface and form a scum which may again be coloured.
For reasons not fully understood, some bloom and scum-forming blue-green algae are capable of producing toxins. Although many blue-green algae blooms are not toxic, some produce nerve or liver toxins and it is therefore safest to assume toxins could be present.
The level of toxicity may vary hour to hour which means it is often not practicable to take regular toxicity tests. In their most dangerous form, both in quantity and species, blooms have caused death in cows, sheep and dogs drinking significant concentrations at the water's edge.
Can the algae be destroyed
Algae feed off the nutrients leached into the water through farm ﬁelds (nitrogen and phosphorous). The only known ways to destroy it are either to ﬁlter all the water and bottom in some way (highly expensive and not 100% guaranteed) or by placing barley straw in the water – again not proven to be 100% successful. It is ﬁltered out of drinking water with sand ﬁlter.
Is it harmful?
The known effects on humans in the UK have been limited to illness rather than death. Since the early 1990's the RYA has had no incidences of illness reported from members following simple safety precautions.
Essentially the more likely you are to come into direct contact with the algal scum, the greater the risk of effects from exposure. Symptoms of those affected could be easily confused with a range of other illnesses so it is important to be aware of the risk of blue-green algae as a contributory factor.
Swallowing and/or inhalation can result in mouth and nose ulcers, blistering of the lips, abdominal pain, nausea, vomiting, diarrhoea, muscular pains, sore throat, dry cough, headaches, hay fever symptoms, dizziness and fatigue.
Contact with the ears and eyes can result in irritation and exposure of the skin can lead to allergic or irritated reactions such as skin rashes, lesions and blisters. Bathing suits and wetsuits can aggravate these effects as the cells can accumulate next to the skin and be broken down through agitation, thus releasing the toxins.
Severe cases could include seizures, liver failure, respiratory arrest and even death, although there are no confirmed cases of human deaths from blue-green algae toxins. The severity of the illness is related to the amount of water ingested and the concentrations of the toxins.
Precautions to take
Sailors are most prone to contact with algae when launching and recovering boats and capsizing in shallow water. If capsize-righting drills are to be performed, it is safer in deeper water where the concentration of algae is lower.
The best way to minimise contact with algae is to wear clothing with tight-ﬁtting seals at the ankles and wrists.
Sailors are advised to wash themselves down thoroughly following activities on the affected water so that scum and algae are removed from their clothing before they enter the changing rooms.
Sailors should clean their hands thoroughly after entering the water and before handling/eating food.
Sailors are advised to thoroughly wash and dry all protective clothing on returning home. Clothes should not be stored wet or damp.
Children, adults and pets should not walk or play at the water’s edge, particularly on a lee shore on a windy day when scum may be found some distance from the edge.
Children or dogs who stray onto the shore should be washed down and in particular dogs should be kept on leads and not permitted to lick scum off their coats.
Is it safe to sail despite the warning?
Concentrations of algae vary from day to day, hour to hour and minute to minute. In particularly hot summers the Health Authorities may deem it so severe that they close that area of water. Otherwise take sensible precautions. Invariably a notice to the effect that ‘blue-green algae is present and they take no responsibility should you enter the water’ is about the only guidance the local Environmental Health Authority will offer! (Land owners have a duty of care to display notices if instructed by the Local Authorities.)