Integrated Water Quality - Western River Basin District 2013

The Western River Basin District (WRBD) is made up of 89 water catchments or drainage systems and includes all of counties Mayo and Sligo, most of Galway and small parts of Roscommon and Clare.  Many of the water bodies are designated protected areas.

Nutrient enrichment (excessive inputs of phosphorus and nitrogen) is the main case of water pollution in the WRBD.  The WRBD is less affected by nutrient enrichment than other river basin districts in Ireland.  In 2013 92.7% of river monitoring stations and 90.7% of lake monitoring results in the WRBD display a high level of compliance with the relevant phosphorus Environmental Quality Standard (EQS).  This compares favourably with corresponding overall national figures of 59 and 59.6% respectively.

western water river basin statistics

Fig. 1 Long-term trend of phosphorus (as ortho-phosphate) concentrations at all river monitoring stations in WRBD.

Since 2002 the overall level of phosphorus in rivers in the WRBD has been decreasing but there remain several examples of unacceptably high phosphorus in river, lake and groundwater monitoring stations.

River sites and lakes in the WRBD with poor biological conditions typically display poor compliance with the phosphorus and/or nitrogen EQSs.  Of the 414 active biological monitoring stations on 211 rivers only 110 stations on 75 rivers (27%) achieve a High classification (Q5 or Q4-5).  It is particularly difficult to reverse the loss of High classification in a stretch of river channel and so it is important that the remaining stretches are protected.

Table 1 Suspected causes of pollution for WRBD river stations in unsatisfactory condition (i.e. biological classification less than Good).

Suspected Pressure
(cause of pollution)

Type of pressureCounty GalwayCounty MayoCounty SligoTotalPercentage (%)
Municipal waste water Point 4 10 4 18 21
Industrial Point n/a 5 1 6 7
Agricultural Diffuse 5 16 5 26 31
Forestry Diffuse n/a 7 2 9 11
Aquaculture Diffuse n/a 3 n/a 3 3
Other n/a 2 2 3 7 8
Unknown n/a 7 4 5 16 19
Total   18 47 20 85 100

Diffuse agricultural pollution (31%) and waste water discharges (26%) are the main causes of river monitoring stations failing to achieve at least good biological classification in the WRBD.  Improved compliance with the Nitrates Directive and improvements in waste water infrastructure and operational practices is required to improve and protect water quality at these sites.  In 16 cases (19%) the source of pollution at the river monitoring station is unknown or not determined.  In these cases investigations are required to identify the sources of pollution and the appropriate mitigation measures.  Implementation of the mitigation measures as part of the revised river basin district management plans will require the co-operation of all stakeholders within a new governance structure to deliver compliance with the Water Framework Directive and protection of water resources in the west of Ireland.

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Integrated Water Quality Report for the Western River Basin District (2013)