WPXI learned that the boy was with a group of children, including his brother, when he fell into the water. Police said the children ranged in age from 8 to 13.
They walked behind Ambridge Sewage Treatment and through the woods to an area where police say kids go to be near the river.
Police said the 10-year-old boy stepped into the water.
"From the story that the brother said, his shoe came off in the water and started floating away, and he tried to go after his shoe," said Rob Gottschalk, chief of the Ambridge Fire Department.
The family didn’t know the children were there, according to police.
The boy’s brother was at first able to grab hold of him and tried to save him, but Gottschalk said the brother's grip slipped and the 10-year-old never resurfaced.
Numerous dive teams, fire departments and police from Allegheny and Beaver counties helped.
Emergency officials even asked WPXI to assist with the search. A state police helicopter joined in, too.
Police said one challenge was the murky water.
“Being that the timeframe is significantly later, it’s going to end up being a recovery,” Gottschalk said.
This is not related to the search for a man who fell in the water near Neville Island on Sunday.