An investigation is under way after more than 400 dead fish were discovered in a County Londonderry river.
The Loughs Agency confirmed it was notified on Monday of a suspected fish kill near Ballykelly village.
Fishery officers were deployed to the scene, where they discovered 422 dead fish, mainly trout, along with several salmon and flounder, across a stretch of about 500m, downstream of the village, beginning just below a discharge pipe.
Although no direct source of pollution has yet been identified, officials believe the incident may have been caused by a "cleaning agent" entering the water system.
In a statement, the Loughs Agency said a detailed investigation was carried out in partnership with the Northern Ireland Environment Agency's (NIEA) Water Management Unit upon the discovery of the dead fish.
Both agencies have urged the public to take extra care to prevent pollutants from entering storm drains, which should carry only rainwater.
"Chemicals and waste products can drastically reduce water quality and cause serious harm to aquatic life," a spokesperson said.
The Loughs Agency added that while the majority of affected fish have been recovered, some may still remain in the river.
Members of the public who come across dead fish in the area are asked not to touch or move them, but instead to contact the Loughs Agency.
The investigation into the cause of the incident is ongoing.