Gardaí are investigating an assault on four men at Mountcharles at about 5.50 am on Wednesday last.
It is alleged that fishery officers were held at gunpoint after they confronted masked men using illegal nets to catch salmon.
One of the officers received six stitches in a head wound after he was struck with a rock.
Inland fishery officers set up a surveillance operation after they spotted the illegal nets in the river Eany in Mountcharles on Wednesday evening.
Noel Carr, Kilcar: "A sad reflection on how bad things are getting in our society when salmon conservation staff are threatened with guns once again."