At sunrise today, the Tennessee River will be filled with hundreds and eventually thousands of athletes.
By sunset, hundreds of those same men and women will be pedaling bicycles in the shadow of Lookout Mountain or running on the banks of the river, pushing themselves to the brink in Chattanooga's second full Ironman competition.
It's the ultimate test of physical endurance for 2,300-2,500 competitors from across the world.
It's also a test for the Scenic City, which once again is putting its outdoor identity on an international stage.
"The overall impact, beyond the financial side, is that it continues to reinforce Chattanooga's name," said Chattanooga Convention and Visitors Bureau President Bob Doak. "It continues to reinforce the brand of this city, and there's not many events I'll say that about."
An estimated 12,000 visitors began arriving last week, some of them as early as Monday. They have been pumping money into local businesses and making their own judgments about the city's outdoor reputation.
The 2014 event earned a 97-percent approval rating from competitors, the second-highest mark worldwide in 2014. It was bested only by Australia's Ironman.
Since then, Chattanooga has been named Outside Magazine's 2015 Best Town Ever and hosted an Ironman 70.3, or half-Ironman event, in which 2,181 athletes competed.
With the growing reputation comes a level of expectation for the 2015 Chattanooga Ironman that businesses and law enforcement agencies have been helping meet.
The biggest bruise to last year's race came on the event's bike path along West Cove Road in Walker County, Ga., where someone spread oil and tacks on the pavement.
"We're just making every effort and taking every precaution to make sure it goes off without a hitch," said Walker County Sheriff's Office Maj. Mike Freeman.
Freeman said officers, including some from neighboring Catoosa County, will work along the Walker County portion of the bike route. The plan, he said, is to keep the bikers safe and minimize the inconvenience for locals.
Police also will focus today's patrols on the area of that 2014 incident, said Ironman operations manager Audra Tassone.
"We're not concerned at all," Tassone said. "Georgia has been amazing. They're taking all the proper precautions to make sure that won't happen again."
Closer to the event's hub, the Chattanooga Police Department supplied 70 officers to support the Ironman over the course of the weekend.
Businesses have stretched their personnel, too, hoping to snag as much of the expected $10.8 million economic impact as possible.
The influx of visitors to the area comes during a post-Labor Day tourism lull, and the average Ironman competitor has an annual income of more than $175,000, Doak said.
"We'll bring everybody on board for (today). It'll be no-holds-barred," said Joseph Montesi, a manager at Blue Plate, a restaurant next to Ironman Village on Chestnut Street. The restaurant plans to extend its hours today. "It'll be exciting. People who normally don't work on weekends like to work and help us out."
The Coldstone Creamery next door also is opening early today and adding staff. A restaurant employee said the store is preparing to serve more protein shakes and smoothies than usual.
"You go to some cities and it's an inconvenience for them," said competitor Chad Henault, a northern Virginia resident. "But this city actually seems welcoming and very supportive."
Friday was the last day for athletes to check in, meaning nearly all of them reserved three nights in a hotel — at the very least. Swarms of competitors roamed around downtown Thursday, the first day for athlete check-in.
"It's nice. It's a smaller city," said Chad Anderson, of Arizona. "We race in Arizona a lot, so we do that Ironman, but it's nice with everything being downtown."
Tassone, the Ironman operations manager, said Chattanooga's downtown is part of what sets it apart from other venues. There is no need to shuttle competitors to and from lodging to the race's start.
"It's a one-stop shop," she said. "They can walk from their hotels to the expos in Ironman Village, they can walk to the restaurants. It's pretty stress-free."
That wasn't lost on 58-year-old Rudy Chavez, who came from the Atlanta area.
"Here, you just go out your door and walk to the start, and you're ready to go," said Chavez, who is staying at the Courtyard Chattanooga Downtown on Chestnut Street.
This is the second Ironman he has competed in. The other was in Switzerland.
Chavez said Chattanooga more than holds its own as an Ironman venue on the world stage.
"The course here, scenically, is awesome," he said. "I'm just hoping to finish and not get an injury — just have a good time and enjoy it."
Contact staff writer David Cobb at email@example.com or 423-757-6249.