Freshwater toxic algae (cyanobacteria) are naturally present in all New Zealand waterways. Usually, toxic algae forms dense blooms when the weather is dry and warm. Algal blooms can be dangerous to aquatic life in our rivers and streams by blocking sunlight and smothering the riverbed.

The bloom will usually last until there is a ‘flushing event’. Flushing events happen after heavy rain, washing the algae away. Once the algae reaches the sea, it is no longer harmful as the salt water de-activates the toxins which affect humans and dogs.