Ireland's State of the Environment Report 2024

201 Chapter 8: Water Hydromorphology Damage to the hydromorphology of our waters is the second most prevalent of the significant issues affecting water quality in Ireland. A significant proportion of our water bodies is being damaged by activities that impact their physical condition, flow and habitat. These changes, referred to as alterations to the hydromorphology, are most common in our rivers and estuaries. The most common types of activities causing hydromorphological damage in Ireland include: ■ channelisation (straightening river channels), drainage and dredging of the waterway ■ land drainage works associated with farming and forestry ■ hard engineering works on the banks and beds of rivers, lakes and marine waters ■ barriers, impoundments and weirs ■ abstraction of water for drinking water, farming and industry ■ overgrazing, poaching by livestock and removal of riparian vegetation. The changes to hydromorphology can impact the entire ecosystem by removing suitable habitat and clogging the spawning beds of fish. Removal of riparian vegetation such as trees can create pathways for pollutants to make their way over land and into watercourses, and reduce shade and food sources for aquatic wildlife. Over-widening of channels can lead to shallower water levels and may result in the overheating of streams and rivers, a risk that is increasing with climate change. Barriers, impoundments and weirs affect the free passage of water and sediment, and can prevent migratory species, such as salmon, lamprey and eel, from accessing their natural spawning grounds and successfully completing their life cycles. Significant water abstraction and land drainage can alter natural flow conditions and lake levels. A reduced flow of water and increased sedimentation can negatively impact species, such as the mayfly and freshwater pearl mussel, that need clean, flowing, oxygen-rich water. 3 www.epa.ie/publications/monitoring--assessment/waste/monitoring-for-per--and-poly-fluoroalkyl-substances-pfas-and- brominated-flame-.php (accessed 25 June 2024). Hazardous chemical substances Certain hazardous chemicals that are widespread in the aquatic environment can cause harm to aquatic organisms and pose a risk to drinking water supplies (see also Chapter 14). These substances are monitored and assessed against environmental quality standards, which have been set at levels to protect the most sensitive aquatic organisms and public health. Of the 349 rivers, lakes and estuaries monitored by the EPA between 2016 and 2021, half had concentrations of one or more chemical substances higher than the relevant environmental quality standard (EPA 2022). Three substances, mercury, polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (PBDEs), accounted for 83% of the exceedances. Mercury is naturally occurring and is emitted globally from volcanoes and the burning of coal. PAHs are produced from the burning of fossil fuels. Both mercury and PAHs find their way into water bodies via atmospheric deposition (rainfall). PBDEs are a group of substances used as flame retardants in the manufacture of household goods and clothing. PBDEs enter water bodies via industrial and municipal waste waters. All three of these substances are bioaccumulative (they can build up in animals or fish), persistent (stable for a long time) and toxic to aquatic and human health. In recent years, other substances of emerging concern have been detected in Irish waters. Per- and polyfluoroalkyl substances (PFASs) are widely used in the manufacture of stain-resistant clothes and household products and in industrial processes and firefighting foams. They enter water bodies via waste waters and leakage from contaminated sites. PFASs have been detected in rivers and estuaries (EPA, 2022), and PFAS contamination has been identified at sites associated with the use of firefighting foams. 3 Pesticides found in our aquatic environment are suspected of having toxic impacts. Concentrations of the agricultural insecticide cypermethrin (a component of sheep dip) were found to exceed the relevant environmental quality standard in some Donegal rivers and transitional waters in the south-east (EPA, 2022). The herbicide MCPA (2-methyl-4-chlorophenoxyacetic acid), used for controlling rushes in grassland areas, is regularly detected in surface waters. In 2023, the pesticide limit was exceeded in 23 public drinking water supplies (EPA, 2024b), mostly because of the presence of MCPA.