Why are the Olympics swimmers assigned a particular lane? A number of them get lane #4.?

Question

Why are the Olympics swimmers assigned a particular lane? A number of them get lane #4.?

Answer 1

mostly the USA team gets lane four, this is because it is the center of the pool...the center of attention, so more people will be watching them.

Answer 2

The center lanes go to the swimmers with the fastest times in the semifinals.

Lane 4: fastest swimmer  

Lane 5: 2nd-fastest

Lane 3: 3rd-fastest

Lane 6: 4th-fastest

Lane 2: 5th-fastest

Lane 7: 6th-fastest

Lane 1: 7th-fastest

Lane 8: 8th-fastest

That way the fastest swimmers are next to eachother and can see how they're doing. They can tell if they need to go faster and if their pace is good.  

Answer 3

Swimmers are assigned specific lanes just to minimize confusion.  The U.S. is assigned a specific lane, as well as the other countries.  It makes announcing the lanes a lot easier.  Often, in both track and swimming, the middle lanes are assigned to the best athletes.