Rising in the Redhole Spring and Wike Head area of Pikenaze Moor in Derbyshire, the river broadens into the Longdendale Chain of reservoirs in the Peak District National Park.

John Stockdale's map published on 12 April 1794 shows the Mersey River extending to at least Mottram, and forming the boundary between Cheshire and Derbyshire.

[4] The upper reaches of the River Etherow pass through peat moorland, inhabited by red foxes, voles and an introduced population of mountain hare.

Longdendale is in the Dark Peak, where a thick blanket of peat overlies the Millstone Grit sandstone, formed on a bed of shale through which flows the Etherow.

At the time of Domesday (1086) the river was firmly established as the boundary between Cheshire and Derbyshire, but the name Edrow or Etherow applied to this upper reach of the Mersey cannot be dated earlier than c.1772.

[8] A packhorse route (known as a saltway) was maintained from the Middle Ages onwards to allow the export of salt from the Cheshire towns of Nantwich, Northwich and Middlewich across the Pennines.

Wool was transported along the turnpike road (1731) that ran from Ashton-under-Lyne, Stalybridge, Mottram, Woodhead and Lady's Cross to Sheffield, to be woven on hand-looms in the dale.

With the adoption of steam to power the ever-larger mills, built closer to the coal fields, the river assumed a new role as a source of water for Manchester and Salford.

In 1844 John Frederick Bateman advised Manchester Corporation that the River Etherow, which rose at the highest point of the Pennine chain, could provide water, collected in purpose-built reservoirs, "nearly as pure as if it comes from the heavens."

[12] The settlement-name Tintwistle, however, implies that Etherow may be an Old English replacement for an earlier name of the *Tin- type (see River Tyne), derived from the hydronym *edre, which is possibly related to ēdre, "vein".

The area was given the designation in 1977 for its biological interest, in particular its wide range of habitats, including open water, tall fen, reed swamp, carr and mixed deciduous woodland.

[6] The Etherow has no major tributaries; it is fed by numerous brooks and streams from the cloughs flowing off Kinder Scout, Bleaklow and Black Hill.