Morgens, Morgans or Mari-Morgans are Welsh and Breton water spirits that drown men. They may lure men to their death by their own sylphic beauty, or with glimpses of underwater gardens with buildings of gold or crystal. They are also blamed for heavy flooding that destroys crops or villages. In the story of the drowning of Ys, a city in Brittany, the king's daughter, Dahut, is the cause, and she becomes a sea morgen.

The morgens are eternally young, and like sirens they sit in the water and comb their hair seductively.^[1] In Arthurian legend, particularly Geoffrey of Monmouth's Vita Merlini, the ruler of Avalon is referred to as "Morgen".^[2] As such, the origin of Morgan le Fay may be connected to these Breton myths.^[3]

Tales of morgens are preserved in the British countryside, even some parts of South West England, like the one from western Somerset, where a fisherman adopts an infant morgen, only to have her revert to the sea when she grows up.^[4]