The tragic drowning of 6 teens in Louisiana happened because the victims and a handful of bystanders all lacked the ability to swim. They're not alone: a full 37% of adult Americans told a CDC study that they couldn't swim the standard lap of 24 yards. A separate University of Memphis study found that about half of American children can't make it out of the shallow end, Slate reports.
The teens in Louisiana were African-American, the demographic the Memphis study found to have the fewest strong swimmers (31%). Economic status also plays a role: a child's ability to swim correlates with the income of his parents—only 29% of skilled swimmers come from families that make less than $49,999 a year.