EPA - Ireland's Environment, An Integrated Assessment - 2020

Chapter 7: Water Quality Figure 7.6  Change in the percentage of high ecological quality (macroinvertebrate) river sites in each survey period between 1987 and 2018 (Source: EPA) 2016-2018 2013-2015 2010-2012 2007-2009 2004-2006 2001-2003 1998-2000 1995-1997 1991-1994 1987-1990 Highest Quality (Q5) High Quality (Q4-5) Percentage (%) of sites Other 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 82.8% 82.4% 81.7% 83.6% 81% 78.3% 76% 74.3% 74.5% 68.4% 16.5% 16.9% 17.4% 14.9% 17.1% 19.1% 20.9% 20.9% 18.4% 18.1% 0.7% 0.8% 1% 1.5% 1.9% 2.6% 3.1% 4.8% 7.1% 13.4% Chemical Status of our Surface Waters While water bodies were mostly at good chemical status, except for the presence of some ubiquitous priority substances, the presence of low levels of some herbicides in rivers was widespread. The chemical status of waters is assessed to ensure that certain chemical substances, known as priority substances, are not causing harm to aquatic organisms or posing a risk to drinking water supplies. These substances are assessed against a range of environmental quality standards (EQSs), which have been set at levels to protect the most sensitive aquatic organisms and to ensure that these pollutants do not end up accumulating in the food chain. Three-quarters of the 322 water bodies assessed over the period 2013-2018 are in good chemical status (EPA, 2019a) (Figure 7.7). This increases to 99 per cent of surface water bodies when ubiquitous priority substances, such as mercury and polyaromatic hydrocarbons (PAHs), which are already widely distributed in the environment, are omitted. The three water bodies that have poor chemical status when ubiquitous substances are omitted are the Owvane river, Co. Cork (which fails for hexachlorobutadiene), the Glenealo river, Co. Wicklow (for cadmium), and the Avoca estuary, Co. Wicklow (for copper, zinc and cadmium). Because of their ability to persist in the environment and bioaccumulate, ubiquitous substances can be found in the environment many decades after international measures have been put in place to reduce or eliminate them. Many are also capable of long-range transport from their place of origin. This means that a ubiquitous substance detected in a water body is unlikely to have come from a source in that water body or even from a source in the surrounding catchment. Information on these substances is presented separately to ensure that their presence does not obscure the presence of other substances that may have arisen from local sources, which can be addressed by local measures. 167