River Hags

Greymoria loathes Mera and enjoys subverting Mera’s Dominion over water by instructing her minions to drown those who displease her. 
River Hags are spirits that were creating specifically to drown people.  They will generally pitch in and aid other Children of Greymoria spirits when the opportunity presents itself but they usually work alone.  They are especially fond of drowning children that wander off alone.
Per their name, river hags usually dwell at dangerous river crossings though they are capable of prowling in and around lakes or the coast of the sea. Their haunts are areas that tend to be treacherous or difficult naturally. River Hags generally exacerbate the natural dangers, not manufacture them.
River hags look like emaciated humanoid crones in tattered rags. They are perpetually wet and dripping water even when moving about dry land.