Threats to Ireland’s lakes

Over recent decades, the pressures on and threats to Ireland’s lakes have been increasing and, as a result, their ecological integrity is often compromised.

Eutrophication (nutrient enrichment), deriving primarily from agricultural runoff is a major threat to the ecological health of many of our lakes, especially those in low-lying situations. The intensification of agriculture, particularly since Ireland joined the European Union, has resulted in greater inputs of chemical fertilisers and more widespread disposal of animal slurry on grassland and arable land. Ireland’s heavy rainfall causes phosphates and nitrates to leach through the soil and into the water bodies that drain into the lakes. This form of pollution has a profound negative impact on the ecology of the lakes, with algal blooms becoming frequent.

Domestic effluent from some wastewater treatment plants and septic tanks has a similar effect, especially where the former are unable to cope adequately with rapidly expanding human population. Extensive use of phosphate-rich detergents (banned or regulated in most other European countries) exacerbates this problem.

Forestry practices, especially on peat soils where heavy application of chemical fertiliser is needed, has caused further nutrient enrichment of the lakes and, in some areas, siltation where drainage channels have been dug down slopes (rather than across them).

The overgrazing of uplands, mainly by sheep (as a result of encouragement through the European Common Agricultural Policy), has also resulted in soil and nutrients being washed down into streams and rivers and, thus, into lakes, often adding significantly to the eutrophication process.

In some parts of the country, lakes have also been polluted to varying degrees with toxic chemicals discharged from various industrial and other human activities (including recreational use of lakes such as boating).

Abstraction of water for human use (domestic, industrial and agricultural) is a problem in some lakes, and is likely to become more serious as the effects of climate change modify rainfall patterns. During dry summers, demand can result in lake levels dropping significantly with concomitant negative impacts on shoreline ecology.

Finally, an increasingly serious threat arises from the introduction, either deliberate or accidental, of non-native species of plants and animals. Many of these exotic (“alien”) species cause little harm to overall ecology, but some are aggressively invasive. The zebra mussel Dreissena polymorpha is now widespread in the Shannon system and has recently spread to the catchments of the River Moy and Corrib which include the great western lakes of Conn, Mask and Corrib. This invasive species threatens the overall ecology of these lakes and is likely to result in the extirpation of some native species (such as the Arctic char Salvelinus alpinus).  The curly-leaved pondweed Lagarosiphon major has invaded Lough Corrib and is already degrading the ecology of many areas of this lake. The American mink Mustela vison, released or escaped from fur farms, has caused widespread declines in waterfowl populations and several species of “coarse” fish have been introduced to some of the lakes with a resultant decline in native salmonid species.