The River Mahon flows through the heart of Kilmacthomas, adding to the village's charm and providing a peaceful natural setting. The river begins high in the Comeragh Mountains, cascades down as the Mahon Falls, and continues its journey through Kilmacthomas before eventually reaching the sea at Bunmahon on the Copper Coast.

In Kilmacthomas, the river is spanned by several bridges, including the impressive railway viaduct that now forms part of the Waterford Greenway. The east bank of the river is known as Kilmacthomas, while the west bank is called Gruaigeshuneen (Gráig Sheoinín).

The Mahon River has a stock of wild brown trout and is popular with local anglers. Salmon run mostly in the autumn and winter, but start running from the early summer depending on conditions.

Visitor highlights

• Enjoy quiet riverside views through the village.
• See the river from the Waterford Greenway viaduct.
• Explore how the river connects Mahon Falls, Kilmacthomas, and Bunmahon.
• Appreciate the river's importance to local landscape and heritage.