Few stretches of water in the world can match the mix of physical challenge and sheer emotional exhilaration that the Bosphorus Strait offers to swimmers making the legendary crossing from Asia to Europe.
Competitors in Istanbul's annual Bosphorus Cross-Continental can ponder stunning Ottoman palaces, modern suspension bridges and 500-year-old military fortresses as they navigate currents first celebrated in ancient Greek myths.
This year, a record 1,500 swimmers aged 14 to 83 who qualified from nearly 50 countries gathered last Sunday for what is still predominantly a “people's swim” for non-professionals rather than a world-class competition.
Turkish authorities shut down the strait, one of the world's busiest shipping lanes, for three hours to allow swimmers time to make the 6.5 km (four miles) crossing. Normally, the only times the Bosphorus closes on a clear day is on the rare occasion a tanker's engine fails or it runs aground.
The Bosphorus has more curves than a belly dancer as it twists through the heart Istanbul, a city of more than 14 million people. It is a swirl of competing currents, and the race's challenge is not so much its distance as charting a precise course through the treacherous flow of water.
Participants in this year's race could not escape the political turmoil that has rocked Turkey over the past weeks.
Some swimmers painted on their bare arms and backs the names of people who died in clashes with police during protests against Prime Minister Tayyip Erdogan's decade-long rule. The protesters say Erdogan is too authoritarian and illiberal, though he remains popular with Turkey's conservative majority.
Erdogan, who has overseen unprecedented economic growth in Turkey and the launch of European Union membership talks, accuses the protesters of trying to destabilize the country.
Dolphins and Jellyfish
The Bosphorus strait features in the Greek myth of Jason and the Argonauts in their quest for the Golden Fleece and its prehistoric formation may have inspired the Biblical tale of Noah's Ark.
The oldest swimmer this year was Levent Aksut, who has competed in all but one of the 25 races since 1989.
These days, Aksut swims the backstroke so he can take in the view.
“The best part is looking at my surroundings and watching the seagulls. Sometimes dolphins will join me, tapping me hard and wanting to play,” he said before the race.
The race began with a sprint from the seaside village of Kanlica to the middle of the channel in search of the southbound stream. The powerful current can reach up to seven knots and virtually halves the length of the race.
Swimmers can see the 15th century Rumelian Castle. Built by the Ottomans in under five months, the fortress aimed to choke off aid to the Byzantines from their Orthodox brethren in Russia. In the end, help never came, and Sultan Mehmet took Istanbul, then known as Constantinople, less than a year later.
In the turquoise depths one considers what might lurk as far as 100 meters below.
In Nobel laureate Orhan Pamuk's novel “The Black Book,” the protagonist imagines the seabed of a drained Bosphorus.
“We shall find skeletons of Celts and Ligurians, their mouths gaping open in deference to the unknown gods of prehistory ... amid mussel-encrusted Byzantine treasures, tin and silver knives and forks, 1,000-year-old wine corks and soda bottles, and the sharp-nosed wrecks of galleons,” he wrote.
Instead, only the occasional jellyfish or stray plastic bag drifted past. Aksut's dolphins were nowhere to be seen.
At the sharp turn at Kandilli, the trick is to stay in the current and avoid getting sucked into bays on either side.
The serpentine strait then widens, and swimmers start to disappear. Depending on one's personality, you might think you were either in first or last place.
If a swimmer is too far out in the channel they risk being swept past the finish line. Those who overshoot hopelessly struggle back against the current.
Aksut was one who had been drawn into a northbound current but didn't mind. It allowed him to enjoy the water a bit longer.
“It's not about how you finish but how much you enjoyed it while it lasted,” he said.