Statlu Lake is about three hours drive east of Vancouver and is renowned for its beauty, although the wilderness is remote and the trail challenging for experienced hikers.
The waterfall has a history of deadly incidents.
Some of the searchers, which include divers, dogs and specialists from Kent Harrison Search and Rescue, had to be flown in on helicopters because of the terrain.
"It's really remote and demanding territory," Rail said. "It is gorgeous but not forgiving."
The search received a strong lead when the missing couple's Silverado ute was found near a hiking trail at Statlu Lake.
Dowsley had been living in Canada for about three years. Her family members immediately flew to Canada when they were alerted she was missing to help with the search.
"It's the worst possible nightmare that you could imagine," Dowsley's father, Peter, told Canada's CTV News. "I couldn't dream of anything worse."
-AAP