The 2016 Olympics officially open with Friday night's Opening Ceremony at Rio de Janeiro's Maracanã Stadium (7 p.m., NBC), an iconic soccer venue that's hosted matches since 1950.

And despite controversies about venues not being ready, polluted water, the Zika virus, and more, the Olympics will go on as planned. Here are five U.S.-centered storylines to follow:

Women's Gymnastics

Who can forget the drama during the 2012 Olympics in London, which ended with American Gabby Douglas winning the women's all-around gold medal and the U.S. women grabbing the team title? In 2016, Douglas is back for more - as is Aly Raisman. It's rare for gymnasts to dominate at more than one Olympics because of the stresses the sport puts on their bodies, but this year we'll see two returnees.

The U.S. women do have some different faces on their roster, of course. Simone Biles is the new star, and she's the favorite on the squad to win the all-around title — which would give the U.S. its fourth straight individual all-around gold medal. Women's artistic gymnastics in Rio begins Aug. 7.

Swimming

He's the greatest Olympian of all-time, given his 22 Olympic medals (18 gold, two silver, two bronze). Michael Phelps retired after the London Olympics and swore to everyone that he was done with the sport. Four years later, he's the first U.S. male swimmer to compete on five Olympic teams.

The 31-year-old Phelps is older and wiser now, has a 3-month-old son, and is engaged to be married sometime after Rio. He's competing in three individual events this month: the 100-meter and 200-meter butterfly, and the 200-meter individual medley. He'll likely be on two relays as well — the 4x100-meter freestyle and the 4x100-meter medley. Swimming events begin Aug. 6.

Women's team sports

The U.S. women's soccer team is looking to win its fourth straight gold medal, while the U.S. women's basketball squad hopes to keep its 41-game Olympic winning streak alive — which dates back to the 1992 Olympics in Barcelona — and win a sixth straight gold medal.

Both squads are heavy favorites in Rio.

The hoops team is led by Sue Bird, Brittney Griner, Tamika Catchings, and Diana Taurasi, while the soccer team has Hope Solo, Carli Lloyd, and Alex Morgan back for another Games. Women's basketball in Rio begins Aug. 6 and women's soccer starts Wednesday.

Track & Field

It's said that the men's Olympic decathlon champion is the world's greatest athlete, thanks to the grueling event that includes 10 individual track & field events over two days. American Ashton Eaton won the 2012 gold medal and won both the 2013 and 2015 outdoor world championship to boot.

In Rio, Eaton is on the shortlist to maintain his status as the world's greatest athlete.

Men's decathlon will be contested Aug. 17-18 and includes the following events: 100 meters, long jump, shot put, high jump, 400 meters, 100-meter hurdles, discus, pole vault, javelin, and 1,500 meters.

Women's Triathlon

Two women are hoping to swim, bike, and run themselves onto the podium in triathlon, a sport that's only been in the Olympics since 2000.

Sarah True and Gwen Jorgensen competed in the London Olympics. They've both enjoyed success since finishing out of medal contention at those Games, and enter the Rio competition as medal contenders.

The U.S. has one Olympic triathlon medal, a bronze in 2004 thanks to Susan Williams. The event involves swimming 1,500 meters in open water, cycling 40 kilometers (24.8 miles), and running 10 kilometers (6.2 miles). The women's triathlon is scheduled for Aug. 20.