A popular Perth swimming spot has been immediately and indefinitely closed after a routine water sampling uncovered a grim find.

The Parks and Wildlife Service of Western Australia announced the closure of Serpentine Falls on Tuesday afternoon.

In its waters, routine testing yielded a positive result for the bacteria Naegleria Fowleri, sometimes referred to as “brain-eating amoeba”.

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The bacteria can cause the rare but potentially deadly infection called amoebic meningitis, which leads to inflammation of the brain.

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The Shire of Serpentine Jarrahdale announced the closure on its website, listing symptoms and a warning.

"Infection occurs where water is forced into a person’s nose at pressure from jumping, falling or diving into the water," the statement read.

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"The following symptoms usually occur within 5 days of infection - severe and persistent headache, high fever, sore throat, nausea, vomiting, neck stiffness, confusion and hallucinations, drowsiness and coma.

"If you or someone you know has been swimming at Serpentine Falls and are experiencing any of these symptoms, please contact a medical professional."

The authority says the swimming spot will be closed until further notice.

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