In Greek mythology, the Naiads (Ναϊάδες from the Greek νάειν, "to flow," and νᾶμα, "running water") were a type of nymph who presided over fountains, wells, springs, streams, and brooks. Naiads were associated with fresh water, as the Oceanids were with salt water and the Nereids specifically with the Mediterranean, but because the 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.
The essence of a naiad was bound to her spring, so if a naiad's body of water dried, she died. They were often the object of archaic local cults, worshipped as essential to humans. Boys and girls at coming-of-age ceremonies dedicated their childish locks to the local naiad of the spring. Oracles might be situated by ancient springs.
Naiads could be dangerous: Hylas of the Argo's crew was lost when he was taken by naiads fascinated by his beauty. The naiads were also known to exhibit jealous tendencies. Theocritus' story of naiad jealousy was that of a shepherd, Daphnis, who was the lover of Nomia; Daphnis had on several occasions been unfaithful to Nomia and as revenge she permanently blinded him. Salmacis forced the youth Hermaphroditus into a carnal embrace and, when he sought to get away, fused with him.