Naiads in Wikipedia
In Greek mythology, the Naiads or Naiades (Ναϊάδες from the
Greek νάειν, "to flow," and νἃμα, "running water") were a type
of nymph who presided over fountains, wells, springs, streams,
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, such as pre-Mycenaean Lerna
in the Argolid.
Naiads were associated with fresh water, as the Oceanids were
with saltwater 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. Arethusa, the nymph of a spring, could make her way
through subterranean flows from the Peloponnesus, to surface
on the island of Sicily...