White Water River ASSI

Protected area type: Areas of Special Scientific Interest
Feature type: 
  • Habitat
  • Down
Council: Newry, Mourne and Down
Guidance and literature: White Water River ASSI

The White Water River has been declared an area is of special scientific interest because of the physical features of the river and its associated riverine flora and fauna.  

The river which has a catchment area of 4253.29ha, rises on the slopes of Slieve Muck and flows into Carlingford Lough near Greencastle.  It is an outstanding example of an upland, oligotrophic (base-poor) river in Northern Ireland with very little human impact and in a highly natural state.  It is of particular note for both the naturalness of the river channel, which exhibits all the physical attributes of in channel features, flow and river bed types typical of the unaltered upland rivers, and the richness of its associated plant community.  Adjoining stands of woodland enhance bank stability and provide food and shelter for associated animals.

The upstream stretches of the White Water River like other Mournes rivers is a typical fast-flowing ultra-oligotrophic type river.  Under these ultra-acid conditions bryophytes and liverworts dominate the channel with common species including Yellow Fringe-moss, Notched Rustwort and Compressed.

The gradient of the river increases further downstream and widens, becoming more dynamic in character and splits in several places producing numerous vegetated and unvegetated mid-channel bars and mature islands.  The river is less acid but the channel is still dominated by bryophytes such as River Feather-moss and Alpine Drab Brook-moss, Water-moss and the liverwort Water, while the banks are more wooded.

In its mid reach the White Water River flows through the estate woodland of Mourne Park.  The flow regime in this reach is characterised by a mixture of riffle, glide, pool and run where the channel has been modified by fishing weirs; and by chute, rapid and riffle along the more natural and unmodified reaches. The channel is rich in bryophyte cover in the more wooded, shaded stretches but is limited in the more open areas where Stream Water -crowfoot , Alpine Water-moss, Drab Brook-moss and Long-beaked Water Feather-moss dominate.

Downstream of Mourne Park the river is characterised by a riffle and run sequences and a few deep pools.  The banks are occasionally bordered by stands of semi-natural woodland dominated by wet Alder woodland in low-lying wet hollows of old river channels with more mature Oak, Ash and Hazel wood on the steep valley slopes where they run adjacent to the river. Aquatic vegetation cover in the channel continues to be comprised of beds of Stream Water-crowfoot and Water Feather-moss.

In the lower reaches of the river, the flow becomes slower and less dynamic and is characterised by run and glide with some extensive areas of riffle. There are few macrophytes in the channel now with the exception of Stream Water-crowfoot and Broad-leaved Pondweed.

The river becomes more brackish in character in its bottom stretch as it flows into Carlingford Lough at The Bents.

The White Water River is of importance for its associated fauna.  Otter are widespread, while Dipper have also been recorded.  Two notable molluscs, the Hollowed Glass Snail and the Ash-black Slug, have been recorded in the river mariginal woodland.

The White Water River has gravel based rapids in the upper reaches suitable for the spawning activity of Atlantic Salmon, Brown Trout and Sea Trout, with the latter being an important genetically distinct anadromous population.  The deeper lower estuarine regions plays host to euryhaline marine species such as Flounder and Bass.  Other species inhabiting the system include the Minnow and the Three-Spined Stickleback. These species frequent deeper pools and slower flowing regions.

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