Fishery Officers tasked with staming out poaching along the Lifford and Strabane river banks have been attacked with knives, hatchets and breeze blocks.
A Loughs Agency official said a member of his staff could have been killed when a breeze-block was dropped from a bridge onto a patrol boat.
The incident, at Lifford Bridge was one of a number of recent attacks on workers carrying out anti-poaching patrols in the Foyle area.
The agency's director of conservation and protection, John McCartney, said workers had been assaulted and had stones thrown at them..
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