With water temperatures hovering around 40 degrees Fahrenheit, monofilament lines tend to stiffen in cold water, often rising to the surface, so it is best to use a thinner alternative. Favorable river conditions to work your flies in spring are behind midstream obstructions and around current breaks.
The most productive hotspots for early spring trout are deep undercutting banks, and especially under trees and overhanging vegetation. You may lose a fly or two, but it is worth a cast. The most popular early season flies for the trout are a Teal and Black, Coachman, Bibbio & Hot orange, Black Pennell and a Connemara Black, though any black fly seems to work well especially if it has a touch of orange and/or white. A Sooty Olive, Fiery Brown, and Golden Olive also produce good results.
The River Boyne holds extensive stocks of wild brown trout and is one of the countries premium brown trout angling waters offering superb fishing.