Olympic Swimming 2012: Michael Phelps and Top Stars on Shaky Ground

Four years ago, the Olympic Summer Games were taken over by American swimmer Michael Phelps. 

After winning eight medals in the 2004 Games, Phelps took home a record eight gold medals in 2008. Many expected Phelps to dominate the pool four years ago. 

Fast forward another four years to 2012, and that domination may no longer exist. The Olympic pool is no longer Phelps' to dominate alone, and he may come up short in what's likely to be his final Olympic Games in London.

In the following slides, we'll highlight Phelps and the other swimmers who could be on shaky ground in London this summer. 

Michael Phelps

A long-running clique in sports centers around the difficulty of repeating as a champion. Getting to the peak is hard, but staying there is an even bigger challenge.

U.S. swimmer Michael Phelps is about to experience that in London this summer. 

After winning a record eight gold medals during the 2008 Olympic Games, Phelps cemented himself as one of the greatest Olympians ever. There's never been a more accomplished swimmer in the long history of the Olympics.

Now, Phelps has stiff competition from Ryan Lochte—a fellow swimmer from the United States—in what is likely Phelps' last Olympic Games. There's going to pressure from across the board in London for Phelps—from his past to the present to the future.

Any slip-ups from Phelps will be more than enough for Lochte to be the man of the summer in the London pools. 

Natalie Coughlin

Natalie Coughlin, 29, has qualified for her third straight Olympic Games, but she may be hard-pressed to add to her 11-medal total this summer in London. 

Coughlin qualified for just the 400-meter free relay, missing out on her other signature events that she dominated in both 2004 and 2008. 

In fact, Coughlin just barely qualified for these Olympics, inching into sixth place in the 100-meter free final at the Olympic trails in Omaha a month ago to secure a spot. 

Missy Franklin

Missy Franklin qualified for an Olympic-high seven events, and there may not be a more well-rounded woman swimmer heading to London from the United States this summer. 

Keep this in mind: Franklin is just 17 years old. She just attended her junior prom. College is a year out. 

And yet, she'll be heading to London with expectations of bringing home gold medals. If she swims in seven events, she'll become the first American woman to do so.

Expectations can crush a young athlete, even if Franklin held up fine (obviously) at the U.S. Olympic trails in June.