Oh, it's a Nickelodeon tv show that aired 2005 to 2008, it is very popular and was recently rereleased on Netflix. It has a decent sequel and a HORRIBLE movie.
It's about the elements water, fire, air, and earth. The only person who can bend all elements is the avatar, and in the series the avatar makes friends and tries to stop the evil fire nation.
HEADCANNON; PERCY CAN ACTUALLY CONTROL A PERSONS MOVEMENTS SINCE PEOPLE ARE 60% WATER, BUT WHEN ANNABETH GOT FRIGHTENED AND HE VOWED NEVER TO USE IT. EVER.