The stream forms part of the border between Cheshire and Shropshire in England to the east, and Wales, particularly the Maelor Saesneg (a detached portion of Historic Flintshire, now within Wrexham County Borough), to the west.

[1] The Emral Brook itself rises near Penley and is joined by a number of tributary streams which drain the central part of Maelor Saesneg.

The middle section of the river valley, which has eroded deeply into an underlying glacial drift of boulder clay, sands and gravels, is the narrowest and deepest, particularly between Dymock's Mill and Lower Wych.

The origin of the name "Elfe" is in this case unknown, though the name "Wych" is thought to derive from saline springs in the area.

[4] It has been speculated that the river name Elfe is based on the Welsh language root hal-, halen, "salt".