The incident occurred on Friday at around 1.20pm when the couple were walking along the banks of the Lombach River with their dogs, cantonal police said in a news release.
When one of the dogs jumped in the 11-kilometre-long river, which flows into Lake Thun, the husband dived in to save the animal but got into trouble, according to the release.
His wife also launched herself into the water but was injured in the flow of the river, the release said, without citing details.
A passerby pulled the husband and the dog to safety, cantonal police said.
The passerby and the husband were able to retrieve the woman from the water and attempted resuscitate her, the Berner Zeitung reported online.
A rescue team arrived at the scene to find her in critical condition.
She was transported to the local hospital, where she died a few hours later, police said.
Investigators are looking into the exact circumstances of the tragedy.
Bern cantonal police, an ambulance team, local fire fighters and an emergency care team responded to the accident, while a helicopter was called for backup.