An investigation has been launched after more than 2,250 brown trout and Atlantic salmon were found dead in a river in County Donegal, Republic of Ireland.
The state agency responsible for the protection and conservation of freshwater fish and habitat said the incident happened in the Glenagannon River in Inishowen.
Inland Fisheries Ireland was alerted to the major fish kill incident by a member of the public via its 24-hour confidential hotline number on Friday.
It confirmed more than 2,250 juvenile brown trout and Atlantic salmon were killed.
The fish kill area covered around four kilometres of the river and comprised several year classes of fish.
Inland Fisheries Ireland said it is following a "definite line of inquiry" to determine the cause, which may result in legal proceedings being initiated.
Its director of the north-western river basin district, Milton Matthews, thanked the person who alerted them promptly about the incident.
"This enabled our environmental team in Letterkenny to instigate our investigations without delay," he said.
"This can be critical in identifying and confirming the underlying cause of fish kill incidents such as this one on the Glenagannon River."