SparkleNinja18's list "Lamiak Names" of 5 great name ideas: Sereia - Vandenė!

Lamiak Names

In Basque folklore and mythology, the lamia (plural: lamiak) was a snake-humanoid creature that was often portrayed to live in rivers. Snake or serpent names are perfect, as are those relating to sirens or mer-people.

The lovely Sereia is the Portuguese word for mermaid but can also be used as a name. English speakers may shy away from the name because of pronunciation questions and indeed, any little Sereia growing up in London or Chicago will encounter many questions and mispronunciations. But it's not difficult to say once you know it and Sereia pay countervailing dividends with its beauty.

Sereia

Sounds like Serena, but refers to the mythological sirens -- half woman, half bird -- who virtually sang men to death. Not a great role model for your little girl. 

Lamiak Names

Sereia

Sirena

Undinė

Uriye

Vandenė