Why are there yellow lanes in the middle of an Olympic swimming pool?

Both lanes 4 and 5 are highlighted by using yellow lane ropes. The swimmers who compete in these lanes have either the fastest entry times or in the case of the final, the fastest qualifiying times. It is an advantage to swim in these lanes as often they are subject to less water turbulance than others. Spectators also can identify swimmers more easily by the use of the yellow lane markings.