Sarah and Ysra Mardini pull bathing caps over their long, black hair and slide into the water, disappearing among the throng of swimmers with powerful, practiced strokes.

Two months ago the sisters were swimming for their lives, after jumping off an inflatable boat that began taking on water carrying refugees to Greece. Now they are ploughing down the length of a pool built for the 1936 Olympics in Berlin that has become a home away from home for two young women, who were once among Syria's brightest swimming stars.

"Everything was good," said 20-year-old Sarah. "That was before the war."

After the conflict began, the Mardini family moved around to avoid the fighting and tried to ensure their daughters could keep on swimming. Ysra, now 17, even represented Syria at the short-course world championships in Turkey in 2012. But as the war intensified fellow swimmers drifted away.

"We were 40 or 50 swimmers, and now we are maybe 10 or 7 swimmers in Syria," said Sarah. "We want to have a future. I want to be in college, I want to be an international swimmer and my sister too. But if we stay there we will not reach that because the situation is not OK in Syria."

The Mardini sisters eventually left Damascus in early August, joining a fresh wave of Syrians who had given up hope of seeing the conflict end soon. The sisters traveled to Lebanon, then Turkey, where they paid smugglers to take them to Greece.

Turkish coastguards drove their boat back on the first attempt. The second time they boarded a small inflatable dinghy at dusk. Within a half hour it was taking on water, hopelessly overloaded with people, most of whom couldn't swim.

As evening winds churned up the Aegean Sea, all bags were thrown overboard to give the small boat a chance to stay afloat. When that wasn't enough, Ysra, Sarah and three others who were also strong swimmers jumped into the water in order to give the boat more buoyancy.

"I was not afraid of dying, because if anything happened I could swim to arrive at the island. But the problem was that I had 20 persons with me," said Sarah. "In Syria I worked in a swimming pool to watch people not drowning, so if I let anyone drown or die I would not forgive myself."

For three hours they clung onto ropes hanging from the side until it reached shore on the Greek island of Lesbos.

In the weeks-long overland trek that followed, strangers gave them clothes, while others stole from them. Friends were arrested at borders and expensive tickets proved worthless, as authorities refused to let trains full of refugees cross borders.

Eventually, the sisters made it to Austria and then Germany. Shortly after arriving in Berlin a local charity put them in touch with the Wasserfreunde Spandau 04, a swimming club based near their refugee shelter.

The club has embraced its newest recruits, putting them straight into a daily training routine.

Sven Spannekrebs, their coach, says the sisters are making amazing progress, though he is realistic about their prospects as athletes. "They can swim at the highest level for the Arab world, but there's a difference to Europe because of the training conditions," he said.

Ysra, who specializes in butterfly stroke, is aiming high. "Maybe when I learn German I will start school. I want to be a pilot," she said. "And with my swimming I want to reach the Olympics."

Her older sister, meanwhile, is battling bureaucracy to bring the rest of the family to Germany. In the pool, she prefers long-distance swimming.

"It seems to me that I have balanced my life," said Sarah. "We can't do anything good in our life if we don't have swimming."