Salmon have returned to the once heavily polluted Tolka River in Dublin for the first time in 100 years.
Successful breeding of the elusive king of fish means the capital has three rivers producing wild stocks.
Dr Ciaran Byrne, chief executive of Inland Fisheries Ireland, said Dublin should boast about the wildlife revival.
“Up to the year 2000 Dublin and Reykjavik were the only two capital cities in Europe which had a wild Atlantic salmon stock in a river within city boundaries,” he said.
“Now Dublin can boast about having three salmon rivers within its boundaries — the Liffey, Dodder and now the Tolka. In environmental terms this is an important step forward.”
Inland Fisheries Ireland said fish surveys indicate the presence of juvenile wild Atlantic salmon in three river locations in the Glasnevin and Finglas areas. Adult fish are also being counted in the Glasnevin area.
It is the first record of wild salmon reproducing in the Tolka for at least 100 years, the authority said.
Dr Byrne said the recolonisation is no doubt linked to reduced pollution levels.
Flood relief works have also helped with the removal or modification of a significant number of man-made weirs to open up the river system to migratory fish.
After work on the Tolka was completed adult sea trout immediately ran the system all the way upstream to its headwaters in Dunboyne, Co Meath, for the first time in at least 150 years.
A study in 2005 found the Tolka was incapable of supporting life because it was so polluted with chemicals.
The Trinity College study found the inner basin of the river had the highest concentration of pollutants in north Dublin Bay with levels of lead, phosphorus and nitrogen so high in one stretch, from Clontarf up to Bull Bridge and Dollymount Strand, that fish and plants could not survive.
Successful river rehabilitation schemes have seen salmon return to the Seine in Paris and the Rhine in Germany, and brown trout to the Wandle in London.