More info;
-Although there were a few found in the Hayseed Swamps, the Kelpies have since then been cleared out of Equestria as far as its most inhabited areas go.
-Kelpies occupy rivers and large bodies of water the most, and can be found in different parts of the world.
Cup the hand above water and slap those gills with all you’ve got.
EDIT: I wonder if these guys and gals may be aquatic cousins of the Changelings?
Edited