Devenish or Devinish () is a lake island in Lower Lough Erne, County Fermanagh, Northern Ireland. Aligned roughly north–south, it is about long and wide.
The island is the site of an early Christian monastery and round tower. It is historically associated with Saint Mo Laisse who is reputed to have founded the monastery in the 6th century. It possibly belonged to the Culdee order. The settlement, which was raided by Vikings in the 9th century, was burned in 1157.
The island, which is accessible by ferry, is in the civil parish of Devenish. The places to catch a ferry include Trory Point and The Round O, outside Enniskillen. Devenish Island is owned by the Kilravock Christian Trust.
Area of Special Scientific Interest
Devenish Island is designated as an Area of Special Scientific Interest (ASSI) for its grassland, which is noted as a significant breeding site location for wading birds, including Curlew, Snipe, Redshank and Lapwing.
Its drumlin landscape also allows communities of scarce plant types to grow there.