WaterNSW declared the red alert Wednesday afternoon, and warning signs have been positioned at recreational sites cautioning those of the danger.

Visitors and residents have been advised not to enter the water, drink untreated water or bathe in water drawn from the storage while this red alert remains in place.

Potentially toxic, blue-green algae can cause gastroenteritis if consumed, whether the water is boiled first or not. Skin and eye irritations can also be an implication.

Those who believe they may have been affected by blue-green algae are advised to seek medical advice.

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"People should not undertake recreational activities where they may be coming into direct contact with the water such as swimming, as well as domestic uses including showering and washing," said WaterNSW in a recent statement.

"Contact with the water may also pose a threat to livestock and pets."

Livestock owners have been asked to regularly check their water supplies for blue-green algae and move animals away from foreshores that they can see or suspect might be contaminated.

People should not eat mussels or crayfish from red alert warning areas.

Any fish caught should be cleaned and washed thoroughly in uncontaminated water before consumption and any internal organs disposed of appropriately.

WaterNSW will continue to monitor the situation however, it is not possible to predict when the algae might dissipate.

Updates and information about blue-green algae blooms and red level warning areas can be obtained by calling 1800 999 457 or visiting - http://www.waternsw.com.au/water-quality/algae

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