At least 2,000 fish have been killed on the Glenmornan River near Artigarvan.
West Tyrone MLA Maoliosa McHugh says the fish kill has affected a number of species, and the final death toll is expected to rise much
further.
Loughs Agency says it has has now identified the source of the pollution and that the Environment Agency is assessing the impact.
Mr McHugh says the impacts of this fish kill will be widely felt:
