The source of the river is just north-west of the village of Knossington, but the Gwash is formed of several small headwaters that come together near Braunston-in-Rutland before passing the site of Brooke Priory at and running westward to pass under the railway Northwest of Manton. The Gwash then helps to fill the Rutland Water reservoir which was formed by damming its valley at Empingham. From the reservoir a controlled flow is released to maintain the flow around Tolethorpe Hall and Stamford and into the River Welland. The flow is enhanced by the Gwash's tributary, the North Brook, at in Empingham, which significantly helps maintain riverlife. East of Stamford, its course is now fixed but it lies in a small flood plain which shows clear signs of the river's former meandering. The pasture fields include depressions which fill in wet seasons forming oxbow lakes, though they are not of the classical shape. Near Stamford it is the parish boundary between Stamford and Uffington. West of Stamford, the Gwash crossed the Stamford Canal, requiring some elaborate hydraulic works. Although the canal has been dry for over a century, the Borderville weir has only just been removed, and some meanders re-watered. The river feeds the millpond at Newstead Mill in the parish of Uffington before entering the Welland at Newstead Bridge just east of Stamford.
Wildlife
The river supports a wild variety of fish species, including grayling and trout. Chub and dace inhabit the lower length below Newstead bridge in Stamford. There are attempts to re-introduce water voles in the area. There are concerns about non-native signal crayfishbecoming dominant in the river, and reports of a deliberate introduction. The river has formed part of pilot control trials.
Etymology
The name appears to be derived from the Old Englishwaesc 'a washing, a flood'. The earliest form was "le Whasse" ; the use of an initial G- is first recorded in 1586 and the spelling 'Gwash' appears to be a quasi-Welsh spelling.
In literature
Local poet John Clare wrote a sonnet about the Gwash, published in Poems Descriptive of Rural Life and Scenery : Where winding gash wirls round its wildest scene On this romantic bend I sit me down On that side view the meads their smoothing green Edg'd with the peeping hamlets checkering brown Here the steep hill as dripping headlong down While glides the stream a silver streak between As glides the shaded clouds along the sky Brightning & deep'ning loosing as they're seen In light & shade—so when old willows lean Thus their broad shadow—runs the river bye With tree & bush repleat a wilderd scene & mossd & Ivyd sparkling on my eye— O thus wild musing am I doubly blest My woes unheeding—& my heart at rest.
