With a victory in the 800, she will join Debbie Meyer as the only swimmers to win the 200, 400 and 800 freestyles in a single Games. But the talent level was baby-pool deep in Meyer’s day. The eight women she beat in the 800 final in Mexico City came from four countries. Forty-eight years later, it is diving-well deep, with seven nations set to be represented in Friday’s Ledecky-led final.

Still, at the last two major international events preceding the Rio Games, Ledecky won the 800-meter freestyle easily: by 6.52 seconds at the 2014 Pan Pacific Championships in Australia and by 10.26 seconds at the 2015 world championships in Kazan, Russia. Her competition on Friday will include many of the same women she vanquished at those meets, with the notable exception of New Zealand’s Lauren Boyle, the runner-up both times, who fell one spot short of the final in qualifying.

For the past three years, Ledecky has geared her training toward swimming fast here. Already, she has broken her world record in the 400 freestyle. And there is no reason to believe that her 800 record of 8:06.68, which is nearly nine seconds faster than the personal best of the next-fastest finalist, is safe.

Sure, Ledecky has raced 2,600 meters, including relays, since the meet got underway Saturday. But having watched her set a world record in bad weather in an outdoor pool at the Pan Pacific Championships, her coach, Bruce Gemmell, said he did not believe the long, late nights of racing here would slow her.