The Quoile Estuary was once a busy port serving the town of Downpatrick, and is associated with legends of Saint Patrick who landed in the area. The Quoile is situated on the southwest corner of Strangford Lough, on the eastern coast of Northern Ireland has a catchment of approximately 242 km2 (approximately 31 % of the whole Strangford catchment). The present impoundment was created by the construction of a tidal barrier across the estuary of the River Quoile in 1957 to relieve flooding problems upstream. Colonisation of the former seashore has resulted in freshwater flora and fauna along the river with some brackish water species resident. The impoundment has been identified as eutrophic and is typically nitrogen limited.