Sergey Fesenko Jr. (also spelled as Sergiy or Serhiy, born June 5, 1982) is a long-distance freestyle swimmer from Ukraine.

His father, Sergey Fesenko, Sr., won the gold medal in the 200m butterfly at the 1980 Olympic Games in Moscow.

[citation needed] Fesenko is a citizen of the United States and As of 2018[update] resided in Indiana.

[citation needed] He served in the Ukrainian military in an Air Defense unit but did not see combat.

It is not known if he has been in active combat, but it is safe to assume he has received incoming fire from Russian forces on these trips.