Simplify the following text for a Grade 5 native English-speaking person.
Original: He steps into the adjoining river and is healed by the waters while Poseidon 's trident appears above his head , revealing him to be the son of Poseidon .
Simplified: He is healed when he steps into a river . When Poseidon 's trident appears above his head , Percy learns that he is Poseidon 's son .