On the Ballisodare river in Sligo, more than 1,000 adult salmon were reported killed in July and the river system, including Lough Arrow, is closed for angling while the government agency Inland Fisheries Ireland (IFI) investigate the cause.

IFI said it is, “awaiting the results of a catchment environmental analysis along with postmortem analysis of affected salmon, in seeking to understand the cause of these deaths. 

“Currently, it is unknown whether or how the cause of these salmon deaths could be impacting other species of fish. The scale of these salmon deaths means we must take every precaution.” 

In late July, on the Aughrim river in Wicklow, some 2,000 fish, including adult salmon and trout, were reported killed. In June, more than 5,000 fish, including salmon and trout, were killed on the River Allow in Cork, and several hundred fish were killed on the River Skeoge in Donegal.

Various reasons for the deaths have been put forward on angling forums, including farm pollution, algae in the sea and high water temperatures, but no cause has yet been identified and IFI investigations continue.