Fabrizio Stabile, 29, from New Jersey, had recently visited the wave pool of a surf resort in Texas.
Kelly Craine, Waco-McLennan County Public Health District spokesperson said, "The CDC collected water samples and are now investigating to find the source".
Stabile showed symptoms of the infection after he visited the landlocked BSR Cable Park's Surf Resort in Waco, Texas. Infections such as the one Stabile had, though rare, happen when the water enters the body through the nose. The fatality rate, however, is more than 97%, with just four people surviving of the 143 reported infections in the United States between 1962 and 2017.
Naegleria fowleri is known as the "brain-eating amoeba" and is usually found in warm fresh water.
When his mother went to check on him in the early afternoon of Monday, Stabile could not get out of bed and could not speak coherently and he was rushed to hospital.
Symptoms start between one and nine days after swimming or other nasal exposure to Naegleria-containing water. "We hope to have results by the end of the week", said Kelly Craine, a spokesperson for Waco-McLennan County Public Health District.
Samples from the pool have been collected for testing, with preliminary results expected later this week. He died at a hospital in Atlantic City on September 21.
She said she didn't know when Stabile was at the park.
He subsequently died of the infection on September 16, according to a GoFundMe page set up to help create a foundation in his honor and to raise awareness of the rare but preventable infection.
There is still no effective treatment for patients infected with this "brain-eating amoeba".
NJ.com reported that by the time he was diagnosed, it was "too late to administer the drug that has been given to three of the only five survivors in North America".