Officials will be looking into why it took an hour and a half to pull boaters from the water after their vessel sank off the west coast of the Island.
The 8.5 metre catamaran began taking on water Sunday, near Bartlett Island.
The distress call came in to the Joint Rescue Coordination Centre at around 1:20. Float plane pilots from the West coast took to the air to search for them, along with Coast Guard and crews from CFB Comox.
The passengers were pulled from the water by privately-owned boats, but had been in the water for more than an hour. Health officials confirmed two had died.
The other three are in stable condition.
Officials will also be investigating what caused the vessel to sink, but RCMP say weather may have been a factor, as the waters off Bartlett Island were described as moderate to rough at the time of the sinking.