Often referred to as Kumköy, the beach resort of Kilyos is quite possibly the best option for watersports within proximity to Istanbul. When the heat of summer hits, you'll find a quite a hefty number of Turks heading to the chilly waters of the Black Sea, particularly the handful of beaches within the vicinity of Kilyos.
There are five beach clubs (whose services come at a fee of up to $20 USD) and the Kilyos Public Beach, all of which fill up quickly in this crowded weekend summer destination. Most watersports will be available here, from jet ski rentals to surfing and windsurfing (especially on Burc Beach, where competitions are held), while each beach will have its own assortment sun beds, umbrellas, and plenty of space for active pursuits like volleyball. Sadly, even on the public beach, there will be fees for nearly everything, so if you're looking for a cheaper way to enjoy a summer day you can always rent a mountain bike and head to nearby Belgrad Forest. Otherwise, resign yourself to enjoying the sun and watersports of Kilyos.
Note:If you don't have a rental car, take the subway to Hacıosman, where there are frequent buses available to Kilyos. Also, if you're feeling a big more of a party vibe, look for DJ's playing in locations like Solar or Tirmata.