The red level warning was announced by the Central West Regional Algal Co0ordinating Committee after routine monitoring by State Water and the NSW Office of Water detected high numbers of potentially toxic blue-green algae at the recreational area.

Office of Water natural resource officer Chris Knight said the warning system was used for recreational areas where direct contact of the water was common.

“It is a naturally occurring organism,” he said.

“On occasions it reproduces in vast numbers and then blooms form.

“Some blooms become so dense that it becomes a problem.”

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

Elevated levels of blue-green algae have also been detected throughout Lake Burrendong.

“The problem is partly because of humans,” Mr Knight said.

“It is from our activity over the years from things like fertilising which, along with other things, puts extra nutrients in the water.

“All we can really do about it is notify people and give them the relevant advice.”

The red level warning indicates the water is unsuitable for recreational use or primary contact by domestic users.

“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,” Mr Knight said.

“It can cause ear infections and in worse-case scenario, lead to formation of a tumour from long-term contact.

“It can also be ingested by breathing the aerosol spray when skiing.

“Boiling the water does not inactivate the algal toxins either.”

Landholders have been advised it may also pose a threat to livestock.

“They should remove stock from the river foreshores as blue-green algae are known to cause stock illness or even death,” Mr Knight said.

“It is the same for dogs as with livestock.

“Dogs are particularly susceptible as they ingest algae by licking their coats, and it has been fatal on occasions.”