The Erriff is a spate river, more noted for summer salmon and grilse fishing than for early season spring fishing. The first fish enter the river around April, and spring fishing starts in earnest in May. Spring salmon run the river in good numbers during May and well into June, although angling effort is usually low at this time of year.

The grilse start entering the river in mid-June and the run peaks in July-August. By July there will be fish in every pool, and fishing can be hectic at times. Like most spate rivers, fishing is best after rainfall, but this being the west of Ireland, that tends to be quite often! Fishing is best in July, August and September, and the back end can produce very good fishing indeed.

The river itself is about 8 miles long, and not a very wide channel, so for summer fishing a single handed 7-8 weight rod tends to be sufficient. For heavy water, a small double hander can come in handy.

The Erriff was once a famed sea trout fishery, but like many rivers in the west of Ireland, it suffered greatly when salmon farms started operating in the nearby bay, and runs collapsed in the early 1990s. In recent years, there has been a strong recovery, and in 2010 sea trout runs were very good. Sea trout start to enter the river in June, and run on most tides throughout the summer. All sea trout caugth must be released alive.