Blooms normally occurred in summer, and it was not clear what had triggered this one, but faeces from Canada geese, which were present in the area in large numbers, could be a factor, as could the lake's current low water level.
She did not think a large fire two summers ago was likely to be a factor. The blaze, which began when a car hit a power pole, wiped out much of the vegetation around the lake.
Raharuhi said the lake was known for its medicinal properties, with its clay in particular used for healing.
Cyanobacteria occur naturally, and are found almost everywhere on Earth. At times, however, they can explode in numbers and become hazardous to people and aquatic life. Blooms are more common in summer in still, shallow water.
They can be triggered by prolonged high temperatures and pollution, such as farm run-off or bird faeces. Cyanobacteria are also called blue-green algae, though they are technically not an algae.
Blooms are also an ongoing problem at Lake Ōmāpere and Kaitaia's Kauri dam, which once provided the town's water.
