The lake water quality of the River Shannon system has improved significantly in the past five years, a report by the Environmental Protection Agency (EPA) has concluded.
The report, by Dr Jim Bowman, an EPA senior biologist, says the main threat to the Shannon's water quality is eutrophication, or over-enrichment by nutrients. Phosphorous, from agricultural activities and municipal waste discharges, is the principal cause of eutrophication. Commenting on the report yesterday, Dr Bowman said the indicators of water quality used improved significantly in the last two to three years. "However, on the other side of the coin, the concentrations of phosphorous in the water, which is another indication of pollution, has improved, but not as significantly as we would have hoped," he said. "We feel the big improvement in the reduction of algal growth is due to the feeding habits of the zebra mussel."
The report says symptoms of euthrophication, such as high chlorophyll concentration and reduced water transparency, have improved. But while there is less phosphorous, the reductions "have not been sufficient to limit plant growth" in the two principal lakes in the system, Lough Derg and Lough Ree. "In the event of a decline in the zebra mussel population, it is likely chlorophyll concentrations will increase again," he said yesterday.
Dr Bowman said there was evidence of significant localised enrichment of the waters of Lough Derg, Lough Ree and Lough Key in 1998 and 1999, despite the apparent overall water quality improvement.
Referring to Lough Derg, the report says the impact of occasional heavy algal growths at the public amenity areas at Portumna, Co Galway, and Mountshannon, Co Clare, was "considerably reduced". "As a result these amenity areas are in a satisfactory condition, with Mountshannon receiving the prestigious Blue Flag award."