長岡市
is a Japanese swimmer, who specialized in freestyle events. She represented her nation Japan at the 2008 Summer Olympics, and has won a career total of two medals (one silver and one bronze) in a major international competition, spanning the Summer Universiade and the Pan Pacific Championships. She set a Japanese record of 54.43 in the 100 m freestyle at the 2009 Japan National Sports Festival in Nagaoka, Niigata. Yamaguchi is a student at Kinki University in Fukuoka.