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.