Why can Percy light a fire at the bottom of the Mississippi River?

Percy can light a fire at the bottom of the Mississippi River because he is a demigod with the ability to manipulate and control fire, thanks to his connection to the god of fire, Hephaestus. Additionally, his powers as a son of Poseidon allow him to interact with water in unique ways, making it possible for him to create flames even underwater. This showcases his extraordinary abilities and the blending of elemental powers typical of his character in the "Percy Jackson" series.