Swimmers beware

Having developed a passion for open water swimming, I have become aware of the health risks of blue-green algae. Known also as cyanobacteria, these micro-organisms are naturally present in water, usually in low numbers, but last year they became abundant enough in Windermere to lead to the cancellation of the Great North Swim.

Cyanobacteria have the distinction of having been found among the oldest fossils on earth of more than 3.5 billion years of age. They are one of the largest and most significant groups of bacteria. Some oil deposits are attributed to their activity, and they are providers of nitrogen fertilisers in the cultivation of rice and beans. Cyanobacteria have also helped to shape the ecological history of our planet in that they generated the oxygen atmosphere on which we depend.

However, some cyanobacteria that can form algal blooms on water produce various toxins, including neurotoxins, hepatotoxins and tumour promoters, such as microcystins. Exposure to blue-green algae on the skin, for example through swimming, may cause a rash or the skin to blister, particularly on the lips or under swimsuits. Inhaling affected water can cause runny eyes and nose, sore throat, asthma-like symptoms or allergic reactions. Swallowing water that contains cyanobacteria can cause acute severe gastroenteritis, liver or kidney toxicity, which may take several days to develop, or neurotoxicity, symptoms of which can appear within 15 minutes of exposure and include dizziness, numb lips and tingling extremities. In dogs, swallowing these toxins has also been linked to convulsions and death.