One of the most important aids to the blind swimmer is the tapper. Standing at each end of the pool is a person holding a long pole with a soft circular ball on the end. As the swimmer approaches they are tapped on the head.
There are several more interesting aspects of the paralympics detailed in an article at the BBC today.
It is a sign to the swimmer that the end of the pool is approaching, and the confidence gained by the tapper's presence means the swimmer can move at full pelt without fearing a painful crash at the end.
"The pole looks a bit like a fishing rod," says Marcelo Sugimori, one of two tappers in the Brazilian Paralympic team. Sugimori used to tap for his sister Fabiana, who won gold in the 50m freestyle in Athens 2004. He now works with the team's two other blind and partially sighted swimmers.
"We tap the swimmer when they are between two and four metres from the end of the pool," he adds. "It takes a lot of training together, and a lot of trust."