It rises near Kirkby-in-Ashfield, and passes close to Pinxton, Ironville, Langley Mill, Eastwood, Ilkeston, Trowell, Stapleford, Sandiacre, Toton and Long Eaton to reach the River Trent near Beeston.
Brewer[1] gives the commonly accepted explanation that it comes from the Old English words irre ("wandering") and wisce ("wet meadow").
This is accepted by Kenneth Cameron, a leading placename expert and Derbyshire specialist, who interprets the name as "wandering, marshy river".
[2] Gelling, who specialises in seeking precise topographical equivalents for toponymic elements, confirms that wisce signifies a marshy meadow[3] but gives only southern examples.
She conjectures that there is an element, wæsse, perhaps Old English, that signifies very specifically "land by a meandering river which floods and drains quickly",[4] and her examples are primarily Midland and northern.
A good example of the meandering character of the river will be seen around Gallows Inn Playing Fields, Ilkeston, where rapid flooding and draining occur frequently.
As it meanders through Toton and Long Eaton the river splits into two sections; the main course veers to the east and the relief channel flows over a low weir in a straight southerly direction.
It passes the basin at the end of the abandoned Pinxton Branch of the Cromford Canal, which shares the valley as the river turns to the south.
During the spring and summer months, the ponds and the watered section of the canal are populated by grass snakes, amphibians and dragonflies.
Butterflies thrive on the wild flowers which inhabit the grasslands, and during the spring, the reserve is a haven for lapwings, beeding snipe, reed buntings and sedge warblers.
[5] Severn Trent submitted a planning application in 2022 to abandon the treatment works and replace it with a pumping station and pipeline to allow the effluent to be treated elsewhere.
[9] Gill Brook joins the river on its left bank, and it is crossed by the Grade II* listed Bennerley Viaduct.
The river threads between the Erewash Canal and Toton Sidings, and is crossed by the railway for the final time to the north east of Long Eaton.
Both are crossed by the A6005 road bridge, before they join again and enter Attenborough Nature Reserve to the south of Beeston, from where the Erewash flows into the River Trent.
Its water supply dropped by a half in 1890, when the London and North Eastern Railway built a tunnel under the Shoulder of Mutton Hill.
[16] Maps show that there were sluices and leats at the site,[17] which was immediately below the confluence of the Nether Green Brook and the Erewash.
John Day's mill is shown on a document from 1814, when it had three pairs of stones for grinding corn, an overshot waterwheel and a drying kiln.
The work cost around £35.8 million, and was designed to improve the quality of discharges into the river system to meet the requirements of the Water Framework Directive.
[26] The route for the pipeline crossed land affected by legacy coal mining, and special permission had to be obtained to lay the pipes through such a high-risk area.
[28] A reference at the beginning of The Rainbow is perhaps the most telling from the geographical point of view: The Brangwens had lived for generations on the Marsh Farm, in the meadows where the Erewash twisted sluggishly through alder trees, separating Derbyshire from Nottinghamshire.
Reasons for the water quality being less than good include discharge from sewage treatment works and runoff from agricultural land.
The closure of Langley Mill sewage treatment works has removed the discharge of treated effluent into the river.
Like most rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE), perfluorooctane sulphonate (PFOS) and mercury compounds, none of which had previously been included in the assessment.