An investigation is under way into the causes behind a kill of up to 1,000 fish on the River Tolka in Dublin.
The kill, which occurred in the Tolka Valley Park area at Dunsink, includes wild brown trout, some of which had been in the river for over four years.
The river had been extensively restocked with brown trout in recent years. Pollution is the suspected cause. The affected stretch is near the Glasnevin Industrial Estate.
Mr Pat Doherty, assistant chief executive of the Eastern Regional Fisheries Board (EFRB), said yesterday that water samples were being taken and would undergo chemical analysis at the Central Fisheries Board laboratory in Glasnevin.
"It is a bad loss. The local anglers are devastated. There were 3lb wild trout among the kill and they would have been spawning this winter. The amount of spawn produced depends on the weight of the fish, so the river has lost a good deal of its reproductive capacity."
Members of the Tolka Trout Anglers' Association were clearing fish from the stretch of the river from early evening on Monday until late that night and again yesterday morning.
The secretary of the association, Mr Eamonn Lynch, described the scene on Monday evening as "painful".
"There were hundreds of fish dead and dying, sticking their heads above water trying to get out of the pollution. Then there were others lying on the bank. Some were wild, two and three pounds so they had evaded capture for a long time, maybe five years, and then this. It has wiped out fishing on the stretch for the rest of the summer."
The association had recently put 600 brown trout into the river as part of its restocking programme. They had also introduced 2,000 brown trout and fingerlings to the river in September last year.
If the source of the pollution is traced criminal charges may be brought, said Mr Doherty.
"The results of the tests should come in two or three days," he said. "Then we will try to source the origin of the contaminant. To bring criminal proceedings, though, will require that the source is identified beyond reasonable doubt."
The pollution would have been exacerbated by the recent hot weather, he said, adding that although the Tolka was often polluted in stretches most of it was clean and could sustain a brown trout population. Urban rivers were always at risk of industrial pollution as rural ones were at risk of agricultural pollution, he said.
