Naiad

In Greek mythology, the Naiads (/ˈnaɪædz, -ədz/; Greek: Ναϊάδες) are a type of female spirit, or nymph, presiding over fountains, wells, springs, streams, brooks and other bodies of fresh water.

They are distinct from river gods, who embodied rivers, and the very ancient spirits that inhabited the still waters of marshes, ponds and lagoon-lakes.

Naiads were associated with fresh water, as the Oceanids were with saltwater and the Nereids specifically with the Mediterranean, but because the ancient Greeks thought of the world's waters as all one system, which percolated in from the sea in deep cavernous spaces within the earth, there was some overlap.

Etymology
The Greek word is Ναϊάς (Naiás,  pronounced  [na͜a.i.ás]), plural Ναϊάδες (Naiades, [na͜a.i.ád.es]) It derives from νάειν (náein), "to flow", or νᾶμα (nãma), "running water". "Naiad" has several English pronunciations: /ˈneɪæd/, /ˈneɪəd/, /ˈnaɪæd/, /ˈnaɪəd/.

Characteristics
They were often the object of archaic local cults, worshiped as essential to humans. Boys and girls at coming-of-age ceremonies dedicated their childish locks to the local naiad of the spring. In places like Lerna their waters' ritual cleansings were credited with magical medical properties. Animals were ritually drowned there. Oracles might be situated by ancient springs.

Naiads could be dangerous. The naiads were also known to exhibit jealous tendencies.