Open water swimming in the Bosphorus

Once a year the Bosphorus — the busy strait that divides Istanbul between two continents — is closed to shipping so that thousands of swimmers can race across it, from the Asian shore to the European side.

It is the only day you can legally swim this water, and the appeal is irresistible: a 6.5-kilometre point-to-point through the heart of a great city, starting in Asia and finishing in Europe, carried along by the strait's powerful current beneath minarets, palaces and the suspension bridges overhead.

Demand far outstrips places, so entry is by lottery, and finishing is a badge of honour among open-water swimmers worldwide. It combines a bucket-list geographic feat, a genuine athletic challenge and the surreal experience of swimming through a normally ship-choked waterway that has been emptied just for you.

A one-way open-water race of around 6.5 kilometres in warm summer sea, made faster by the strong surface current — though that current, and the need to hit the right line to reach the finish, is exactly what makes it tricky.

You start in a mass entry off the Asian side and aim across and down the strait to the European shore; swimmers who drift wide can miss the finish and be pulled from the water at the cut-off time.

There is real chop, boat wake, and the mental challenge of a long swim with no touching bottom. Safety craft line the course.

You need to be a confident, fit open-water swimmer able to cover the distance comfortably — it is welcoming in spirit but a serious swim, not a paddle.

The swim is held once each summer and entry is by lottery through the Turkish Olympic Committee, opening months ahead — register in the window and be ready for disappointment or a place.

Train specifically for continuous open-water distance well beyond 6.5 kilometres in a pool or lake, and practise sighting and swimming in a wetsuit or skins as the rules require. Learn to read and use the current line, ideally with tips from past finishers, since navigation decides many swims here.

Arrive early for registration, timing chip and the ferry to the start, and respect the cut-off time. You must be a strong swimmer and meet the organiser's age and qualification rules; this is not the place to attempt your first long open-water swim.