Kelpies are the mini-bosses of the Shrine of Water in Zelda's Adventure. They appear as green women who serve the Shrine's Keeper, Agwanda.
Zelda faces three Kelpies throughout the Shrine of Water. The South Kelpi is first fought just shortly after the wooden bridge, the North Kelpi is fought second, and the East Kelpi is fought third in the flooded passage of the later part of the Shrine. The Kelpies must be defeated in order to proceed through the dungeon and to reach Agwanda, as their defeat will remove Floor Spikes that block the way ahead.
The Kelpies can be defeated with the Turquoise Ring Spell, and take four hits of its projectiles to defeat. Since the Spell is very costly to use, Zelda should be advised to aim her Spell carefully to conserve Rupees. They can also be defeated normally with Zelda's Wand, but requires many consecutive hits.
Kelpi likely comes from Kelpie, a shape-shifting water spirit that is commonly described as appearing as a horse, but can assume human form. It may also be derived from kelp, a type of seaweed.