An announcement about the deaths of Megan Scraper, Alexey Lyakh, and Ryker Gamble came on the "High On Life" group's Facebook page.
Gamble and Lyakh were two of the co-founders of a Vancouver-based collective - High on Life SundayFundayz - who regularly posted videos of their extreme adventures around the world.
RCMP said on Tuesday that the trio slipped and were dragged into the current while swimming in one of the pools near the top of the falls on the Upper Shannon Falls hiking trail.
Mangelsdorf said Gamble died trying to help Lyakh.
Gamble, 30, and Lyakh may have died trying to save Scraper - who was the first to fall, the Vancouver Courier reported.
The victims were all in their 20s and 30s.
A delicate search and rescue operation stretching into two days turned into a recovery mission.
The deaths were confirmed by Ryker, Megan, and Alexey's friends from High on Life.
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"There are truly no words that can be said to ease the pain and the devastation that we are all going through right now", he said in the video.
One of Gamble's family members also confirmed that he was among those killed.
The group also launched a GoFundMe page to help the trio's families with arrangements.
At almost 1,100 feet, Shannon Falls is the third-tallest waterfall in British Columbia. One video from their channel is even titled, "Epic Cliff Jumping and Waterfall Slide (EXTREME DANGER)".
A search and rescue effort underway in Squamish to locate three people who reportedly went over Shannon Falls and failed to resurface in Squamish, July 3, 2018.
The group has run in to trouble for their dare-devil antics.
In 2016, Gamble and Lyakh were banned from a host of USA national parks - along another group co-founder Justis Price Brown - after walking on a sensitive hot spring in Yellowstone National Park.
Gamble and Lyakh pleaded guilty to heading off the walkway at the park and onto the Grand Prismatic Spring. Lyakh and Gamble were reportedly sentenced to seven days in jail and banned from accessing USA public lands for five years. They were ordered to pay fines and served a week in jail.
In a subsequent apology they spoke of being drawn to a natural wonder.