The two women died late Sunday morning on the Skokumchuk rapids, about 60 kilometres north of Sechelt., B.C.
The RCMP said four members of the Royal Canadian Marine Search and Rescue were heading through the rapids in a boat when the accident occurred.
"We've since learned that two of the occupants passed away as a result of the accident," said RCMP Sgt. Mike McCarthy.
Capt. Annie Djiotsa, a spokeswoman for the Royal Canadian Navy, said the victims and the two survivors — both men — were in a rigid hull inflatable boat when it overturned.
The rescuers who pulled the men to safety were members of the same volunteer organization and were in a nearby boat, said McCarthy.
The two victims were residents of Sechelt and their bodies have been removed from the scene, said McCarthy.
According to a Navy media release, the bodies of the deceased were found under the hull of the capsized boat, and the two volunteers were pronounced dead at about 1:15 p.m.
The boat was tied up at a local dock Sunday afternoon, and members of the Transportation Safety Board of Canada were headed to the scene to investigate, McCarthy said.
Peter Sly, fire chief of the Egmont and District Volunteer Fire Department, said he watched the rescue from his home and saw several boats trying to respond to the overturned inflatable.
Sly said the rescue lasted more than two hours and drew the Canadian Coast Guard vessel Cape Caution, a Buffalo aircraft, Cormorant helicopter, members of the Royal Canadian Marine Search and Rescue from Pender Harbour, B.C., as well as local boats.
Sly said the area can become dangerous, especially when tides as large as 5.5 metres rush through the narrows of the local inlet, forming waves and whirlpools.
At the time of the accident, the current was running at about 13 nauts, said Sly.
"Several people have lost their lives over the years in the rapids," he said.
Keith Ashfield, the minister of fisheries and oceans, said he was saddened by the deaths and offered his condolences to the victims' families, friends and crew members.
"As search and rescue partners there to protect Canadians on the water, the Canadian Coast Guard shares the pain of this tragic loss," he said in a statement.
Royal Canadian Marine Search and Rescue, formerly known as the Canadian Coast Guard Auxiliary, is a volunteer organization with more than 1,000 members and stations in 46 B.C. communities.
The organization said it responded to 700 missions in 2011 and helped more than 850 people.
---by Keven Drews in Vancouver