The each uisge is an Irish Water Horse.
Etymology
Irish Gaelic "each uisge"
Description
They were supposed to come out of the sea and Gallop along the shore or through the fields. It appears as a horse to be ridden. Anyone who could catch one and lead it away from the shore could use it as a splendid mount, if not the finest steed to be ever seen. But, if it came within sight or sound of the sea, it would gallop wildly into the depths and either drown or tear its rider to pieces, and devour them eating all but the liver.. It is said that its skin is adhesive so that the rider cannot pull themselves off it.
Family
It belongs to the same family of water horses as the Scottish each uisge and the aughisky and bears some relationship with the Welsh ceffyl dwfr. It should not be confused with the beautiful, lake-dwelling horses Cúchulainn captured and trained; he returned those to their mountain pool of his own volition when they were mortally wounded. The shoopiltee is a variant of the each uisce from the Shetlands.
Place
The water-horse inhabits salt water or large still bodies of inland water, and is thus distinguished from the kelpie inhabiting running water.