Routine monitoring by the NSW Office of Water and State Water has detected high numbers of potentially toxic blue-green algae at Carcoar Dam.

A Red Level Warning indicates that waters are unsuitable for recreational use or primary contact by domestic users and may also pose a threat to livestock.

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 inactivate algal toxin.

Algal blooms can develop in a 24 hour period and can spread rapidly along the river.

Local residents and visitors should avoid any water that appears bright green, where obvious green scums are present, or a distinctive odour is noticeable.

Blue-green algae are usually very obvious, appearing as clumps or specs in the water and are often associated with a strong musty or earthy odour.

People are advised not to enter the water, and are further advised not to drink untreated water or bathe in water drawn from the river whilst a Red Level Warning is in place.

Landholders are advised to remove stock from the river foreshores as blue-green algae are known to cause stock illness or even death.

Dogs are particularly susceptible as they ingest algae by licking their coats.

Livestock owners are reminded to continue to check stock water supplies for blue-green algae and to remove stock from foreshores where surface scums are visible or blue-green algae are suspected.