Serhiy Anatoliyevich Serhieiev (also Serkan Atasay, Ukrainian: Сергій Анатолійович Сергеєв; born March 11, 1970) is a Ukrainian-born Turkish swimmer, who specialized in butterfly and individual medley events.

[1] He is a three-time Olympian (1996, 2004, and 2008), a multiple-time Ukrainian champion, and a five-time Turkish record holder.

[2] Eight years later, Atasay qualified again for the 200m individual medley by clearing a FINA B-cut of 2:03.01 at the Ukrainian Open Championships in Kyiv.

[3] Swimming in heat four, he edged out Barbados' Bradley Ally to take a third spot and 22nd overall by 0.03 of a second in 2:03.26.

[7] He competed against six other swimmers in the second heat, including two-time Olympian Miguel Molina of the Philippines.