Thirty fish kills have occurred in waters around Donegal in the past seven years, according to a new report from the EPA.
The Inland Fisheries Ireland office in Ballyshannon registered 30 kills in its catchment area between 2010-2017, with 18 incidents still unexplained.
A fish kill is a sign of a catastrophic ecosystem disruption, said the EPA.
The presence of healthy fish stocks, particularly salmon and trout, in rivers, lakes and estuaries is an indicator of good water quality.
There are many possible causes for a kill, but oxygen depletion in water is said to be the principal reason for fish kills. These conditions can be brought about by organic pollution from agricultural, municipal and industrial sources.
The known causes of fish kills recorded at Ballyshannon between 2010 and 2017 are varied.
Five were from agriculture practices, six from municipal works, one from industrial operations and the causes of 18 other kills were undetermined.
IFI Dublin recorded the highest number of fish kills (57) in the same period.
There were 14 fish kills recorded in Ireland in 2017, affecting 7.8 km of river with 2123 dead fish recovered. This figure is seen as a positive drop from previous years. There were 31 fish kills in 2016
Fish kills are recorded as one of 16 indicators of water quality in Ireland’s rivers. The new EPA indicators report has found that water quality in Irish waters has deteriorated between 2015 and 2017, despite some improvements.
197 river water bodies have improved in quality but 269 water bodies have deteriorated compared with the last full assessment in 2013-2015.
Most pollution is caused by too much nitrogen and phosphorus entering waters, the report said.
One of the highest recordings of winter phosphorus concentrations were found in the Erne Estuary in Co. Donegal, where phosphorus values were 0.04 mg/l P.
Phosphorus, if present in sufficient concentration, can cause eutrophication (effects of nutrient
Despite a long-term reduction, recent data from the EPA indicates that levels of nitrogen and phosphorus are beginning to rise again across Ireland. Unless addressed, this is likely to lead to further declines in water quality in the future.
Overall, the report found the serious pollution is continuing to decrease. Only two river water bodies were seriously polluted in the latest reporting period compared to five in 2013-2015. Historically there were 91 seriously polluted water bodies in the late 1980s.
Commenting on the report, Dr Matt Crowe, Director of the EPA’s Office of Evidence and Assessment said: “Clean, healthy water is essential to our health and wellbeing. The signals in this report are not good and tell us that water quality is still getting worse in some areas despite improvements in others. This is simply unacceptable. We must do more to halt deterioration in water quality so that we protect this most precious public resource.”