The presenter's pain and suffering was etched across her face and she had to cling on to her support team's kayak as she was overcome with the effort and the cold of her open water swim.
McCall, 46, was limp with her head lolling as she was dragged from the water after reaching a jetty as concerned organisers rallied around her, carrying her clear and wrapping her up.
But minutes later was seen warming up in a hotel room and about to get her hands around a mug of hot chocolate in a photograph posted on Twitter, and her core temperature was said to be on the way back up.
The presenter is attempting to travel 500 miles under her own steam as she heads from Edinburgh to London by running, swimming and cycling.
Within hours of setting off on Saturday morning her team was concerned she was exhibiting signs of hypothermia as she battled severe weather during a tough 130-mile stint in the saddle.
But after being examined she was cleared to continue with her seven-day journey, the BT Sport Relief Challenge: Davina - Beyond Breaking Point.
Yesterday she scaled Scafell Pike, where she again faced treacherous weather, trudging through snow and negotiating her way through the cold mist.
In previous years brave celebrities have put themselves through other draining pursuits for Sport Relief. David Walliams picked up stomach bugs during his swim down the River Thames, as well as developing sores from his wetsuit, and two years ago John Bishop was left in agony amid worries about stress fractures as he did back-to-back marathon distance runs en route from Paris to London.