The boy fell in the river at Lützefluh on Saturday and was pulled out of the water downstream by passersby, cantonal police said in a statement.
An emergency doctor called to the scene attempted to revive the toddler but could only note that the child was dead, according to the staement.
The toddler apparently got separated from his family without them knowing it, police said.
Lützefluh is located in the Lower Emmental region through which the River Emme flows.
Police said they were seeking further information to find out exactly what happened.