Suspected blue-green algae (cyanobacteria) has been sighted in the Albert Town lagoon.
The Otago Regional Council are now testing samples of the toxic algae found at the lagoon, with results expected by Thursday.
Visitors are advised not to use the area for recreational purposes, and to observe the warning signs, while dog owners are also being warned to avoid allowing their pets to swim or go near the water.
Cyanobacteria can produce toxins that are harmful to humans and animals if swallowed or through contact with skin. Exposure to cyanobacteria may cause symptoms such as skin rashes, nausea, tummy upset, and tingling and numbness around the mouth or tips of fingers.
Meanwhile, the Otago Regional Council have lifted the health warning which was in place at Lake Waihola, where high concentrations of the algae were found, and the lake is once again safe for public use.
Anyone experiencing health symptoms after contact with contaminated water should visit their doctor and also contact Public Health South on (03) 4769800.
Cyanobacteria occurs naturally but can increase rapidly during summer months. If the water is green or has floating bright green or blue scums, all contact should be avoided. Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the bloom has disappeared.
