Twitter user///////// aka Miroku, posted a video to the microblogging site showing a member of the Waseda Water Ski Team taking a practice run on the Tone River.
A fish suddenly jumps out of the water and strikes the man in the genitals. The water skier manages to hold on for a few seconds before he has to let go of the rope.
"The fish struck the crotch," Miroku wrote in Japanese.
The tweet quickly went viral, with tens of thousands of retweets.