The zebra mussel, which is threatening the river Shannon, has now spread downstream to Limerick docks. According to the latest ESB Fisheries Conservation's annual report, 8,000 out of 1.2 million salmon fry died when the water level dropped in one of the tanks at Parteen hatchery after the zebra mussels blocked the inlet pipes. The mussel was first reported in Lough Derg in 1997. The report also says that salmon stocks on the Mulkear River have almost fully recovered following the major fish kill in August 1997.