Swimming Precautions

Father and son walking in water

Naegleria fowleri, also known as the “brain-eating ameba,” occurs naturally in freshwater bodies, such as lakes, rivers, and hot springs. Infections with Naegleria fowleri are rare, and they occur mainly during the warmer months of July, August, and September.

If water containing the ameba goes up a person’s nose, the ameba can enter the brain and cause a rare and devastating infection called primary amebic meningoencephalitis (PAM), which is almost always fatal.

Naegleria fowleri thrives and multiplies in warm water

In the United States, infections have most often occurred after people went swimming or diving in warm fresh water, such as lakes and rivers. Sometimes infections have happened after people put their head under water in hot springs.

Infections usually occur when temperatures are hot, which results in higher water temperatures and lower water levels.

Because Naegleria fowleri is very common in the environment, public health officials can’t control levels of the amebae that naturally occur in fresh water. The location and number of amebae in the water can vary over time within the same lake or river.

In very rare instances, Naegleria fowleri has been found in inadequately chlorinated water, including in pools, splash pads, and a surf park. Naegleria fowleri is not found in salt water, such as the ocean.

Take precautions while enjoying water activities in fresh water

Most Naegleria fowleri infections occur in young boys, although the reasons for this aren’t clear.

It’s possible that young boys are more likely to participate in such activities as diving into the water and playing in the sediment at the bottom of lakes and rivers.

People should always assume there is a risk for infection whenever entering warm fresh water. The only sure way to prevent an infection is to avoid water-related activities in warm fresh water, especially during summer months.

If you choose to swim, you can reduce your risk of infection by trying to prevent water from going up your nose.

  • Avoid jumping or diving into bodies of warm fresh water, especially during the summer.
  • Hold your nose shut, use nose clips, or keep your head above water when in bodies of warm fresh water.
  • Avoid putting your head under water in hot springs and other untreated geothermal waters.
  • Avoid digging in, or stirring up, the sediment in shallow, warm fresh water. The amebae are more likely to live in sediment at the bottom of lakes, ponds, and rivers.

Seek medical attention if you or someone you know develops a headache, fever, or vomiting after swimming in fresh water. Initial symptoms of PAM start about 5 days after infection but could begin anytime from 1 to 12 days.