Common blue-green algae produce toxins which can cause gastroenteritis and skin and eye irritations. Animals have died from drinking algal scum, and there are concerns that algae-produced liver toxins could promote live cancer in humans.
Because they are photosynthetic and aquatic, cyanobacteria are often called "blue-green algae". This name is convenient for talking about organisms in the water that make their own food, but does not reflect any relationship between the cyanobacteria and other organisms called algae. Cyanobacteria are relatives of the bacteria, not eukaryotes, and it is only the chloroplast in eukaryotic algae to which the cyanobacteria are related.
Blooms of blue-green are increasingly reported in reservoirs and waterways in the UK and Australia. Toxins released by the algae can kill animals and cause nausea, diarrhoea, skin rashes and minor liver damage in humans. Toxins in contaminated reservoir water are not removed by water treatment plants with conventional sand filtration, and even modern activated carbon filters are not always effective. Algal blooms are most common in late summer and autumn, promoted by warm water conditions, sunlight and high levels of nutrients.
In 2000, the Swan River in Perth was indefinitely closed to the public as a result of a bloom of highly toxic blue-green algae. All water-related recreational activity was banned.