Istishia

Istishia (pronounced is-TISH-ee-ah ), also known as King of Water Elementals, is the neutral primordial deity of elemental water and purification.

Worshipers
Istishia is worshiped by Sailors, Pirates, Water Elementals, Water Genasi, some Aquatic Elves, and others who feel a bond with the Ocean's destructive power.

Relationships
Istishia allies are those deities with a relation to water, like Deep Sashelas, Eldath, Valkur, and Umberlee, but they are not strong relationships. He opposes Kossuth in every way.

Advanced Dungeons & Dragons 1st edition (1977-1988)
Ed Greenwood initially used Straasha, one of Moorcock's Elemental gods as found in the original Deities & Demigods, as the elemental lord of water for his home Dungeons & Dragons campaign set in the Forgotten Realms. As Greenwood indicated in his article "Down-to-earth Divinity" in Dragon #54 (October 1981), Moorcock's elemental gods "may later be replaced in [his] universe by "official" AD&D beings as these are published". Istishia first appeared in the original Manual of the Planes (1987), and was featured as one of the elemental lords for the Forgotten Realms in the Forgotten Realms Campaign Set's "Cyclopedia of the Realms" booklet (1987).

Advanced Dungeons & Dragons 2nd edition (1989-1999)
Istishia was described in the hardback Forgotten Realms Adventures (1990), the revised Forgotten Realms Campaign Setting (1993) in the "Running the Realms" booklet, and Faiths & Avatars (1996).

Dungeons & Dragons 3rd edition (2000-2007)
Istishia appears as one of the major deities of the Forgotten Realms setting again, in Forgotten Realms Campaign Setting (2001), and is further detailed in Faiths and Pantheons (2002).

Dungeons & Dragons 4th edition (2008-Present)
Istishia appears in the fourth edition as a primordial.