CHICAGO Olivia Smoliga has competed at the very highest levels of swimming in the most pressure-packed environments the sporting world has to offer.

But even the two-time Olympian, who has a gold and a bronze medal on her impressive resume, admitted she had a little nervous energy when she went to bed Saturday night.

Smoliga, a Glenview native who attended Glenbrook South High School before competing in two Olympic Games, was one of 300 swimmers jumping into the Chicago River on Sunday morning for a historic swim. The Chicago River Swim marked the first time since 1927 that a sanctioned open-water swim has been held in the river.

With no lightning in the area and a water quality test conducted Sunday morning turning out OK, the event was given the go-ahead.

The first competitors began their swim at 7 a.m. Sunday. Smoliga was scheduled to be among the swimmers who began at 8 a.m.

“No qualms about getting into the river. I’m excited,” said Smoliga, who won a gold medal in the 2016 Rio de Janeiro Games and a bronze medal in the 2020 Tokyo Games. “I went to bed with a little bit of nervous energy, but after seeing the first wave of 2-milers jump in, I’m pumped.

“I’ve always been drawn to the water. I see any body of water, and I want to be in it. So I really couldn’t pass this up.”

The course

The Chicago River Swim course consists of a half-mile stretch along the river’s main channel, between Wolf Point and the State Street Bridge.

There are two distances, a longer 2-mile course and a shorter 1-mile course. All swimmers must have qualified by participating in other swim races, such as a triathlon.

The course is also marked with large inflatable buoys, and lifeguards are positioned throughout it. No boats will be allowed on the river during the swim, either, which the Coast Guard will make certain of.

Last year, the swim was moved to the lakefront after the city denied a permit for the Chicago River over safety concerns and swimmer concentration. But the City Council gave its blessing last month for this year’s swim to be held in the river.

Organizers were out Friday morning running a safety check and setting up the 1- and 2-mile routes.

Swimmers, at least according to Smoliga, will choose whether to attack the course from a strictly competitive mindset, or to just enjoy some of the scenery.

“I’m looking forward to, if I can, taking a peek of beautiful downtown, maybe doing some backstroke under the bridges,” Smoliga said. “I don’t know if I’m going to be much of a competitor (Sunday).

“I’m not an open-water swimmer, so that competitive juice might fire off. Or I might just enjoy the views all around me.”

The cause

The Chicago River Swim is also a fundraiser for ALS (Lou Gehrig’s Disease) research. A Long Swim, a nonprofit organization founded by open-water swimmer Doug McConnell, is putting on the event.

McConnell has lost his father and a sister to ALS. Some of the money raised at the Chicago River Swim will benefit Northwestern University’s Feinberg School of Medicine.

McConnell told WGN-TV he shed a tear when the first swimmers got into the Chicago River on Sunday morning.

“We’ve been working on this for so many years, and to finally see so many swimmers in the water is such a treat,” he said. “It’s just a dream come true.”

A Long Swim has raised $2.5 million for ALS research to date.

“The ALS researchers over at Northwestern’s med school are superstars, and the progress that they’re making is really remarkable,” McConnell said. “We’re just thrilled to be able to support them.”

Additionally, the Chicago River Swim will raise money for The Salvation Army Croc Center Chicago to help provide swim lessons for kids.

And while all the swimmers probably have different goals in mind Sunday, they’ll all have one thing in common as they navigate the Chicago River Swim course.

They’ll be part of history.

For Smoliga, who said she began training in New Trier about four weeks again and is on track to compete in the 2028 Olympic Games in Los Angeles, it’s a one-of-a-kind swim.

“I’m really excited, and it’s events like these that keep my spirit fresh,” she said.