Jason Russell narrated the Kony 2012 campaign video which went viral on the internet last week.
According to police, Jason Russell had been detained and taken to a medical facility.
In a statement, Invisible Children head Ben Keesey said that a “severe emotional toll” had led to an “unfortunate incident”.
The statement said Jason Russell had been hospitalized on Thursday “suffering from exhaustion, dehydration, and malnutrition”.
San Diego police spokeswoman Andra Brown told AFP news agency: “Officers responded to a radio call to check the welfare of an individual who was said to be running in the street, interfering with traffic, screaming.”
Andra Brown added that after assessing his condition, officers had decided to take him to a medical facility for treatment.
It has the backing of countless celebrities and the International Criminal Court’s chief prosecutor, but both the group and the video have also come under heavy criticism.
Activists say the campaign simplifies a complex issue, and questions have been raised about Invisible Children’s financing.
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