Kali Hardig is in critical condition with a rare meningitis caused by the microscopic amoeba. She got violently ill just days after playing at the park.
The CDC believes she picked it up while swimming at Willow Springs Water Park in Little Rock. The parasite thrives in rivers and lakes and kills 99 percent of people who contract it.
There have only been 50 known cases of the disease reported in the last ten years in the US.
Three years ago, a 7 year old boy died after being infected at the same lake. The owners of the water park have shut it down, possibly for good.