Search efforts continue for a fourth day as a girls' summer camp confirms 27 children and staff are dead, with 10 campers and one counsellor unaccounted for.

There will be time to sort out whether the tragedy could have been averted, but the devastation is still unfolding, and it is already unfathomable.

More than 850 people have been rescued by emergency responders. Many of the stories have been astonishing: A Coast Guard swimmer saved 165 people at the summer camp; a 22-year-old woman was rescued after being swept 20 miles downriver and clinging to a tree overnight; and a young girl was found after floating on a mattress for hours.

Texas Hill Country, where much of the flooding took place this time, is often referred to as “flash flood alley.” It's home to steep terrain and a lack of vegetation that creates a perfect storm for waters to rise quickly.

At least 81 people, including more than two dozen children, died in the torrential downpour. Dozens more were still missing three days later.