The primary species of cyanobacteria found in Otago are Phormidium, which can occur in rivers, and blue-green algae, which can occur in lakes. Both species can produce natural toxins that can be a risk to human and animal health. 

Cyanobacteria alerts for rivers are currently in place for the Cardrona River and the confluence of Dunstan Creek and the Manuherikia River, while in lakes alerts are in place for Tomahawk Lagoon, and, as of today, for Falls Dam. With staff anticipating the potential of a bloom at Falls Dam, additional testing was also carried out downstream from the Dam. Test results for these sites on the Manuherikia River are clear, indicating that the bloom is currently confined within the dam itself. Signs have been placed at Falls Dam to warn the public of the risks associated with the blue-green algae. 

Exposure to cyanobacteria may cause symptoms such as skin rashes, nausea, tummy upset, and tingling and numbness around the mouth or tips of fingers. Anyone experiencing health symptoms after contact with contaminated water should visit their doctor. Southern DHB Medical Officer of Health can be contacted on (03) 4740999 to provide health professionals with information about those symptoms.