Aquaphilia also called hydrophilia is a form of sexual fetishism

Sexual fetishism

Sexual fetishism, or erotic fetishism, is the sexual arousal a person receives from a physical object, or from a specific situation. The object or situation of interest is called the fetish, the person a fetishist who has a fetish for that object/situation. Sexual fetishism may be regarded, e.g...

 that involves images of people swimming or posing underwater, and sexual activity in or under water.

Literally "water lover" from the Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 aqua and Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

φιλειν (philein), the term "Aquaphile" was first used by Phil Bolton, when he created the "Aquaphiles Journal" - an online magazine for followers of the underwater erotica scene published in the 1990s.

The psychology of Aquaphilia was the subject of a paper by Dr. Corinne Lamberth (a therapeautic counsellor based in Lewisham, South London) in 1998. A copy of this paper was published in the Aquaphiles Journal in early 1999.