Flash floods surged through in the middle of the night, but many local officials appeared unaware of the unfolding catastrophe, initially leaving people near the river on their own.

Before the floods came, Camp Mystic’s sprawling 700-acre campground was dotted with green-roofed, cobblestone cabins and rows of cypress, live oak and pecan trees. After, bed sheets tangled in broken branches. Muddy clothes, an overturned canoe and other belongings from campers remained.