Two brothers -- just 2 and 4 years old -- are dead after they were found unresponsive in a river, authorities said.
The incident unfolded when concerned witnesses called 911 at the Kankakee River by the Illinois and Indiana state line on Tuesday, said Lake County Sheriff Oscar Martinez Jr.
Witnesses said the boys' father was in and out of consciousness and "acting strangely," Martinez said at a news conference Wednesday.
The witnesses "felt that he was under the influence of something," Martinez said, and noticed him "jumping in the water. And the witnesses were confused of where the kids were at and started looking for the kids."
Witnesses found one child floating in the water and the second child under the water and unresponsive, he said.
The boys, Evan Patillo, 2, and Levi Patillo, 4, both died, Martinez said.
The boys' mother has been contacted, Martinez said.
Their causes of death are under investigation, he added.
"It's a tragedy," Martinez told reporters. "It hits us hard."
The boys' father, Eric Patillo, was interviewed at the Lake County Police detective bureau, Martinez said, and was then taken into custody and booked on two probable cause charges of neglect of a dependent resulting in death.
Authorities are awaiting test results that would reveal if Patillo was under the influence of alcohol or narcotics, Martinez said.