There are over 12,000 lakes in Ireland, some very small and some quite extensive.  Most are located on the western seaboard and in the midlands and are relatively shallow.  Generally water stays longer in a lake than in a given stretch of river and so lakes are prone to over-enrichment if the nutrient load is high.  This can lead to the excessive growth of algae and slimes that can damage fisheries and limit the use of the lake for amenity purposes.

Lake Classification

The level of nutrients in a lake determines its trophic status and, using that measure, lakes are classified as follows;

  • Oligotrophic – poorly nurished, poor plant growth.
  • Mesotrophic – small amount of nutrients, little plant growth.
  • Eutrophic – considerable amount of nutrients, excessive plant growth.
  • Hypertrophic – very high levels of nutrients with corresponding high levels of plant growth.
It is important to remember that some level of nutrition is required to support natural background levels of plant and animal life but when too much nutrition reaches a lake then problems arise.

Lake Quality

Overall, Irish lakes are in very good condition.  They predominantly support salmon and trout fish, both of which are very sensitive to pollution.  The most recent survey by the EPA placed 92.1% of lake surface surveyed in the oligotrophic or mesotrophic categories with a further 7.7% classed as eutrophic and 0.2% hypertrophic.

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