An LAFD spokesman made the announcement at the scene about 5:45 a.m.
Jesse Hernandez was reported missing the previous afternoon, prompting a massive response from multiple agencies.
The initial report came in just before 4:30 p.m. of a 13-year-old boy who fell into a drainage pipe that feeds into the river. More than 100 firefighters were searching the water near the 5200 block of W. Zoo Drive with no sign of the boy.
The drainage ditch is about 13 feet wide and two feet deep, with swift moving water.
Officials said Jesse and some friends had climbed a chain-link fence and were playing in an abandoned maintenance shed near the river when a wooden plank gave way, opening a hole that led into a drainage pipe and the boy fell in. The water was moving fast, about 6-10 mph, officials estimated.
More than 20 members of the Hernandez family were attending a picnic in the Griffith Park area at the time as part of an annual Easter tradition.