THERE has been a dramatic drop in the number of rivers with high-quality water over the past two decades.
Septic tanks and accidental releases of pollutants are among the reasons why just one-in-four rivers have "pristine" water quality today compared with 41pc in 2000, a report from the Environmental Protection Agency (EPA) says.
One-off housing, field drainage, faulty septic tanks and over-grazing are also factors.
The report – 'Management Strategies for the Protection of High Status Water Bodies' – says that in 2000, some 285 of 686 rivers monitored were of "high" status, or 41pc.
That fell to 270 rivers, from 987 monitored, in 2010/2011 – down to 27pc. It is highly likely that lakes have also been affected.
"While serious pollution has decreased significantly in the period 1987–2008 . . . there has been a dramatic loss of the best quality, high-status sites," the report adds.
"Rivers best illustrate this; however, there is no reason to suppose that lakes in such catchments are not also impacted by many of the same pressures."
Other key findings included:
• More than 10 high-status sites have been lost in each of the following counties – Cavan, Clare, Cork, Donegal, Galway, Leitrim, Mayo and Sligo.
• However, of the 210 sites lost in this timeframe, 27pc were lost in Donegal.
Among the rivers and water bodies under threat is the Caragh in Co Kerry, which runs within the Killarney National Park and Macgillycuddy's Reeks.
The river drains the southern slopes of Macgillycuddy's Reeks before it enters Lough Caragh and flows into Dingle Bay.
In 2009, just two out of 39 sites surveyed were of high status. The report says there has been a "significant deterioration" in the condition of the river since 2007, mostly caused by over-grazing, forestry and use of pesticides and septic tanks.
One of the report's authors, Fiona Murphy, said that tighter planning controls were needed.
"It is important to note that the smallest pressure can impact on water bodies that are in pristine condition," she said.
"The input of a few grams of phosphorus or a slight increase in silt, for example, will have a much more damaging impact on the ecology of a pristine system than the same addition to an already polluted system. The research findings clearly point to the need to develop and implement measures to protect high-status, pristine water bodies from becoming degraded."