Two days before flash floods on the Guadalupe River in Texas killed dozens of campers at a Christian girls summer camp, a state inspector approved operations, noting there was a written plan for responding to natural disasters.

Several hundred people gathered at Tivy High School’s stadium in Kerr County, Texas, to mourn the victims of the catastrophic flash floods that hit the region and to honor the many still missing.

Henry DeHart, interim president and CEO of the American Camp Association, said counselors typically receive training in areas such as risk management, emergency procedures, child development, abuse pr...