Water NSW has issued a red alert level warning for blue-green algae for Lostock Dam.
The high level warning warning means people should not swim or undertake recreational activities where they may come into direct contact with the water.
Water NSW has advised the water should not be used for showering and washing.
Contact with the water may also pose a threat to livestock and pets.
People are advised not to enter the water, not to drink untreated water or bathe in water drawn from the dam while this red alert level warning is in place.
Town water supplies remain unaffected and safe to drink.
Warning signs are at key recreational areas of the dam and will remain in place while high levels of blue-green algae are present.
Livestock owners are reminded to continue to check stock water supplies for blue-green algae and to remove stock from foreshores where surface scum is visible or blue-green algae are suspected.
People should not eat mussels or crayfish from red alert warning areas.
Any fish caught should be cleaned and washed thoroughly in uncontaminated water and any internal organs disposed of before consumption.
The species of blue-green algae identified are potentially toxic and may cause gastroenteritis in humans if consumed and skin and eye irritations after contact.
Boiling the water does not remove algal toxins.
The Hunter Region dam is sitting at 97.2% capacity with any significant rainfall likely to move algal concentrations downstream in the Paterson River should the dam spill.
Blue-green algae usually appear as green paint-like scums on the water, near the edges, or as greenish clumps throughout the water. It makes the water appear dirty, green or discoloured and generally has a strong musty or earthy odour.
Blue-green algae occur naturally and can reproduce quickly in favourable conditions where there is still or slow-flowing water, abundant sunlight and sufficient levels of nutrients.
Water NSW has advised it is not possible to predict how long the algae will remain at high levels.
Regular monitoring will continue, and the alert will be lifted as soon as the high levels of algae dissipate.
People who believe they may have been affected by blue-green algae are advised to seek medical advice.
Updates about blue-green algae blooms and red level warning areas can be obtained by calling 1800 999 457 or visiting the website – http://www.waternsw.com.au/water-quality/algae