Lake Wyangan has been put on red alert for blue-green algae.
Griffith City Council has advised the northern part of the lake is on red alert following a sample taken on February 5.
As a result, people should not undertake recreational activities where they may be coming into direct contact with the water, such as swimming.
They should also refrain from domestic uses including showering and washing.
According to the council, contact with the water may also pose a threat to livestock and pets.
Warning signs have been positioned at key recreational areas and will remain in place while high levels of blue-green algae are present.
People are advised not to enter the water, drink untreated water or bathe in water drawn from the Lake while the warning is in place.
Before consumption, any fish caught should be cleaned and washed thoroughly in uncontaminated water and any internal organs disposed of appropriately.
Council is monitoring the level of Blue Green Algae on a regular basis and provides updates via the website: https://www.griffith.nsw.gov.au/lake-wyangan-water-quality