WaterNSW on Friday issued a Red Alert warning for high levels of potentially toxic blue-green algae for the Barwon River at Mungindi.

The alert also extend extends immediately upstream and downstream of the township, however water users further along the river should apply a high level of caution as the algae will likely move downstream due to river flows.

The Red Alert warning applies only to untreated water at the identified location and will remain in place until monitoring confirms that the risk is sufficiently diminished.

People should not consume untreated water. Boiling the water does not remove algae toxins.

People should avoid recreational activities such as swimming, water-skiing, canoeing and any other activity that brings them into contact with water from the dam until the red alert warning is lifted.

Toxic blue-green algae may potentially cause gastroenteritis if consumed, while contact can cause skin and eye irritations.

Consumption of water containing algal toxins may cause liver damage and other health problems. Boiling the water does not remove algal toxins.

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

A precautionary approach to eating fin fish from red alert warning areas is advised.

Any fish caught should be cleaned and washed thoroughly in uncontaminated water; the internal organs should not be eaten.

Avoiding fishing during a bloom is the best way to minimise risk.

Individuals who suspect they have been affected by blue-green algae should seek medical advice.

Blue-green algae is naturally occurring and can reproduce quickly in still or slow-flowing water when there is abundant sunlight and sufficient nutrients.

Visit the local council or local water utility websites for information about the management of blue-green algae risks in the nearby treated drinking water supplies.