In the very flattest and wettest areas of Tireagan peat bogs have formed often filling the natural bowls created by the underlying granite.
There are a few small areas of marsh in Tireragan generally associated with lochens and patches of wet woodlands in gully bottoms.
Peat bogs are characterised by their dominance of Sphagnum moss but are also home to insectivorous plants such as sundew and butterwort as well as grasses such as deer grass and cottongrass.
Throughout the world many peat bogs have been dug up to provide the very fertile peat compost often used in gardens but has also been an important fuel on the Hebridean islands where, once dug up and left to dry, peat is as surprisingly good fuel for fires. In many areas of Tireragan one can still see signs of past peat diggings.
Surrounding some of the lochens at Tireragan are areas of marsh dominated by Phragmites reeds while there are also a few sheltered marshy areas at the bottom of wooded gullies that contain plants more familiar to lowland marshes such as marsh marigold.