Water-wizards

"If the enemy did not laugh themselves away, it was said that Mother Rhoyne would whisper the enemy's secrets to her children and the Rhoynish wizards could raise watery walls to drown their foes."

- Varys

The Rhoynish water-wizards were powerful worshippers of Mother Rhoyne.

History
During the Rhoynish Wars, Mother Rhoyne was said to whisper the secrets of the Rhoynar's enemies to them, allowing the water-wizards to raise walls of water with which to drown their foes. The water-wizards used the same magic to raise enormous water spouts to defeat the dragons of Valyria.

In the books
In the A Song of Ice and Fire novels, the water-wizards were said to have defeated the Valyrians by flooding Volon Therys, washing away half the city.

Despite not being a witch, Queen Nymeria was called a "witch queen", as it is said that when she brought her people to Dorne she had Rhoynish water-witches whose secret spells made dry streams flow again and deserts bloom.

It is believed that the hammer of the waters summoned by the greenseers of the Children of the Forest may have been a form of water magic.