A 29-year-old Swiss citizen and a 34-year-old Spaniard fell out of a rubber boat after it struck the pillar of a wooden covered bridge on Sunday afternoon, Bern cantonal police said in a news release.
According to initial findings the women went under water for a long time after the raft collided with the abutment, the release said.
The women were fished out of the river with the help of other rafting participants and passersby, cantonal police said.
Passersby resuscitated the women on the river bank before rescue workers arrived.
Two ambulances took the women to hospital, where they later died, police said.
The Swiss victim was identified as a resident of the canton of Valais, while the Spanish woman was a resident of the canton of Vaud.
They were with a group of people in several boats.
The local prosecutor has launched an investigation into the exact causes of the accident.
The victims were not wearing life jackets “but that is not an obligation with this kind of boat,” Alice Späh, police spokeswoman is quoted as saying by the ATS news agency.
The accident occurred in a section of the Aar that is known to be calm but choppy waters can occur near the pillars of the bridge, a regular river rafter told the agency.
River rafting on the Aare between Thun and Bern is promoted as a tourist attraction.
Typical trips with inflatable boats or canoes cover 28 kilometres and take three to four hours, Switzerland Tourism said.
The latest two fatalities bring to at least 32 the total of drowning victims in Switzerland this year, five more than during the entire year in 2014.