The Hawke's Bay District Health Board is warning people to avoid contact with the water at Lake Tutira following the possible sighting of cyanobacteria bloom on the lake.
Medical Officer of Health Nicholas Jones said the Hawke's Bay Regional Council had tested the bloom and was waiting for final results, which were unlikely to be available until early next week.
Mr Jones said eating fish from the lake should also be avoided as fish could accumulate toxins from the bloom in their gut. If people did choose to eat the fish they should make sure all of the gut and liver was removed and the fish was thoroughly washed before cooking.
Warning signs have been put in place and the public are urged to stay away and to keep animals away from the lake until the warning is lifted.
Temporary signs warning swimmers against bathing were also erected in January this year, after several families were left with severe skin rashes after coming into contact with the water over the festive break.
* Cyanobacteria are single celled creatures that live in water environments and have characteristics in common with both bacteria and algae.
* In warm, nutrient-rich conditions free-floating cyanobacteria cells can multiply quickly to form what are known as algal blooms. Large numbers of the bacteria can also grow as mats on river and lake beds and these mats can sometimes detach and float to the surface.
* Some species produce toxins (cyanotoxins), which pose a risk to humans and animals when consumed in drinking water or by direct contact during recreational activities.