RIO DE JANEIRO — At the Olympic swimming pool, the world’s best swimmers are never more than a few strokes from the pool wall and always within reach of a buoyant lane marker. They are constantly watched by countless coaches and assistants.

Also watching? Lifeguards. The Olympic swimming pool has lifeguards, just in case someone like Michael Phelps, winner of 18 gold medals, needs to be rescued.

“I’m dreaming of that possibility,” Anderson Fertes, a 39-year-old health-club lifeguard from Rio, said with a smile before starting his pool deck shift at the Olympic Aquatics Stadium. “I think about that.”

The odds are small. “It’s a one-in-a-million type of event, but we’re prepared,” Fertes said.

The lifeguards at the Rio Games have perhaps the best view in the house, as they are among the few people permitted on the pool deck. But they might not feel particularly useful.

During a training this week, Phelps cruised past, stroke after stroke, lap after lap, training for the competition that begins on Saturday. The arena was mostly empty, with just a smattering of coaches, volunteers and security guards. But watching most intensely from opposite sides of the pool deck were two men in red trunks, with whistles around their necks and flotation devices tucked beneath their arms.

They never used their whistles. They never once yelled at the Olympians to stop running on the pool deck. They never flinched toward action, or even felt their hearts skip a beat faster at the sudden and momentary possibility — is she still underwater? — that someone might need saving.

“I don’t think they’ll need us, but we’ll be on the lookout just in case,” Fertes said.

By appearance, the Olympic lifeguards are of the same breed as those who coolly oversee the high jinks at the community pool and are prepared to dive in to rescue a struggling or sinking swimmer. There are about 75 of them, including 15 women, hired to work the Olympic sites and training centers for swimming, diving, synchronized swimming, water polo and white-water kayaking. (Patrolling the open waters for events like triathlon, marathon swimming and sailing is a separate matter.)

A lifeguard might come in handy in a few events. Water polo can get ruggedly physical. Synchronized swimming is a surprisingly frequent source of sports concussions. Divers risk smacking the water.

But at the swimming pool, 10 feet deep, for events like the 50-meter sprint and the breaststroke? They need a lifeguard or two?

“Yes, it’s necessary,” said Danielle Martelote, 25, the lifeguard supervisor at the Olympic Aquatics Stadium. She cited the possibilities of debilitating cramps, heart attacks and head-crunching collisions with the wall.

“We hope they don’t need our intervention,” she said.

Certainly no swimmer has died at the Olympics, but it is less clear if a competitor has ever required a lifeguard rescue. Still, lifeguards are a common, if overlooked, sight at world-class swimming events, such as the recent U.S. swim trials in Omaha, Nebraska.

FINA, the sports’ international governing body, does not explicitly require lifeguards at the Olympics.

Eight lifeguards, including Fertes, were assigned to swimming. Since training began at the start of last week, and until competition begins on Saturday, they split two shifts. Four of them — two at the competition pool, two at the training pool — work from 8 a.m. to 4 p.m. The other four then take their places and work until training ends at midnight. They are paid about $340 for about 20 days of work.

The lifeguard schedule for the Olympic events — who gets to be on the stadium pool deck for the premier events (watched by millions around the world on television) and who must work the training pool (which the public does not see) — has not been determined.

But Martelote and some of her charges kept close proximity and a sharp focus on Phelps as he trained on Tuesday. He was the one they watched most intently.

“We joked to each other, ‘We’re here to save him!’” she said. “But we hope and expect that all the athletes will be fine.”