The western part of Lough Derg is crossed by the north-south road at which the villages of Mag Mell, Mardagh and Tir na mBeo are located. In the lake is the Dergan Island, which is inhabited by the Dergans. In the zone Lough Derg, the river forms a big lake and leaves it in the south of the zone to flow towards the sea. The lake is nurtured by the waters of the river Shannon, which crosses the Zone Connacht too, but vanishes into impassable mountains before reaching the lake. The landscape, with its rolling foothills is divided by the big lake Derg, after which it's named.

If there is a geographical center of Hibernia, it is Lough Derg.